Remember, 'i' before 'e' except after 'c'; isn't English wierd like that?

Yes. And it is the exception, rather than the norm.

No, that's just basic logic. You wouldn't write hi's or her's, why in the world would you write it's?

That's not a rule, that was some idiot trying to apply Latin grammar to English (in Latin it's not actually possible to do), and apparently failing to realize that English isn't Latin. Safe to ignore that.

In any case, yes, it's annoying because if someone is doing a job, and you are paying that person, it's reasonable to expect that person to do the job correctly. Especially with something that's really not that hard to do. If you skipped out after third grade, hire a proofreader.

Oh definitely. I'd rather see offers to buy consumables for real money than ignorant misspellings. (I'm more tolerant of typos.)

The full hierarchy of terribleness (less is worse):

7. British spelling.
6. American punctuation.
5. Technogenic typos: "serislizer".
4. Ignorant misspelling of individual words: "seperate".
3. Word and part of speech misuse: "You could of done this".
2. Lies: "his 16-year-old husband" instead of "his husband of 16 years" ; also : French spacing !
1. "what the hell is wrong with you" assbackwards ideas: "A three-man activist group has set out to make the world a better place by stealing famous pieces of art in the world's most renowned museums, selling them to private collectors, and donating the money to charity."
0. asbsluuut lak of fukn efort

8: Comma trouble: The thing saving you from eating your grandma. (Let's eat, Grandma! vs Let's eat Grandma!)

Gulp! (Grandma has (been) eaten.)

You're in combat with a dragon, and you've got time to immediately recognise a spelling/grammar/punctuation mistake in a combat log...

"If you can keep your head, while others around you are losing theirs, then you obviously DON'T UNDERSTAND THE SITUATION!"

There are many ways this could happen. For example:
* The game could be turn-based, giving you all the time in the world to check the combat log. Or the game could be real-time with pause, and you have paused the game.
* You could have just happened to notice the mistake out of the corner of your eye.
* You died, and are checking the combat log to see what killed you. (This is something that's possible in many roguelikes (including the DS version of Shiren the Wanderer), though it is unfortunately not possible in Baldur's Gate (that's one thing the EE *should* have fixed, but from what I heard, didn't).)
* The dragon in question is weak enough that it's a non-threat, and it's rather boring fighting dragons like this all the time, so you decide to look at the combat log.

That's strange. Grandpa's been dead for a year.

TXT fucking type it's "YOU" not "U" it's "ARE" not "R" it's "I'll kick you in the nuts for it" not "Illkikuindanuts4it"

it's either "Your or You're" not "ur"

I feel like cutting people up with a fucking chainsaw when they type like that, It's one of my major pet peeves it really riles me up.

Doesn't break the immersion MORE than "2d6=7: -14HP". Should it ?

[1] Actually, the "made up rules" are the result of evolutionary forces in the cognitolingual workspace. English is the world champion language for borrowing other languages' vocabulary, idiom and even spelling. (The problem was less pronounced before spelling was fossilized — when Modern English appeared. Douglas Adams parodied this in THHGTTG with his "Gin & Tonic" observation.) For example, Cardith (in Wales) and Cadiz (in Spain) are two polities with almost identical phonemic origins. In Europe, (ever since the invention of the Alphabet) the EI digraph is universally pronounced like the stuff ungulates eat, i.e., the vowel in "hay", except in the German Sprachtbund, wherein it sounds like the English optical organ, e.g., like the vowel in "high" (ignore the leading H).

When a new dialect emerges, called a creole, it tends to hybridize the parent/s. Latin is a synthetic language, wherein each part of speech exactly identifies its purpose. English is an analytic language, which uses word order to determine semantics. Italian, like all the Romance languages, being a creole, has some analytic features (like prepositions).

So, English is almost totally unique in that it borrows directly from other languages — including spelling (!) — and then native speakers (scilicet, those who only speak one language), try to back-form a pronunciation in isolation.

Punctuation was developed much later, after (roughly in chronological order) word spacing, and the minuscule (lower case) lettering.

Punctuation is only important if you wish to improve the reader's experience. Any writer who wishes to assist the reader with comprehension has a few (mainly graphical) tricks to deploy, but punctuation is significant.

Having a system means that one may read something written by an unknown author and understand (maybe with some textual analysis) what is meant. Unequivocally. (For example, legal judgments can be predicated on the placement of punctuation.)

If there is a system, there are rules. If there are rules, they can be broken accidentally and purposefully.
[2] A possessive pronoun needs no apostrophe, like theirs, so the distinction is salient.
It might be a better idea to stop using the apostrophe for a possessive. (In a hundred years, how will people write?)

Actually, as far as I can tell:
* A possessive *noun* needs an apostrophe: "John's", "Mary's", "the table's legs" (note that "legs". when the plural of "leg" has no apostrophe, but the possessive "leg's" does need onw)
* A possessive *pronoun* does not have an apostrophe: "his", "her", "its", "my", "your", "their". Notice that these forms tend to be les regular; many don't even end with an "s".
* It just so happens that "its" has a homophone "it's", which is a contraction that is equivalent to "it is". Similarly, "their" has homophones "there" (a term used for a location) and "they're" (contraction for "they are"). If you notice, many of the common English mistakes involve using the wrong homophone in writing; in spoken language, this mistake doesn't exist.
* Some dialects of English have nonstandard contractions like "I's" (I is) and "ain't" (am not); these contractions are not homophones of standard English words, and therefore tend not to be used accidentally by people not using those dialects.

You know what ruins immersion? The wrong music!

Playing a Commandos game with blaring trumpets is a no go. I usually turn the music completely off for 90% of the games I play.

Yes, the confusion is complicated because, in English, an apostrophe indicates both a plural (noun) and also the omission of letters, as in the word fo'c's'le (videlicit, the pseudo eye-dialect phonemic transliteration of the crew's living quarters below decks in the bow — known as the forecastle, but pronounced as per the apostrophes). In this instance, the apostrophe/s indicate a contraction in an aid to pronunciation.
Yet another (completely contrary) use of the apostrophe is to indicate the plural for of a borrowed word. This is probably the genesis of the dreaded greengrocers' apostrophe, as they were merely introducing a foreign word to their customers, hence banana's means "several of a tropical fruit new to Elizabethan England (and Modern English)", which were never seen before Cavendish imported them.
As has been noted, these grammatical peculiarities are not a problem in spoken idiom; literacy had penetrated less than 2% of the populace until modern times.
A lot of modern vernacular writers use nouns adjectivally. (This is especially prominent in the USA: California raisins, instead of Californian, for example.) Is suspect this is yet another idiomatic adaption, either by the monoglottal Anglophones (as a mistake) or the polyglottal migrants, to lessen confusion (between noun and adjective forms of a word). (If I had to bet, I'd wager the monoglots are at fault, since their language skills are significantly impaired.)

English really needs some consolidation (and ingenuity) in its use of punctuation. Unfortunately, literacy, punctuation, and spelling all fossilized with the appearance of Modern English. However, that doesn't mean new idioms cannot develop; the subtle difference between imply and infer was only militated in the 1970s (so, for example, Jane Austen is blind to it). (And, on point, the use of an apostrophe to indicate a decade, as in 1970's, has dropped out of fashion in the meantime, too.)

Also, to answer the OP: it depends.
If the mistake is buried in a log where it's not easily visible, then, No. (It will bug me, but as long as I can distract myself playing, then I can ignore it.) Far more catastrophic, for example, is the missed apostrophe in the VERY FIRST LINE of the beginning of Dex. I have lost several microns of tooth enamel from my molars because of it. :)