Yes, "for now" albeit i would not be that sure about not wanting to drink blood, and, more like, eat brains. Being that big, have own Apis. client, paying audience and lot of publishers can turn later in huge problems.
Lets take a look at mobile market, Google Play. Goddammit, not only "FREE" but now paid games now stuffed with tons of "in-app purchases" or so called micro-transactions. Why& easy to use apis, easy access to customer wallets.
What if PC games will turn in same? Like you playing FPS, you out of ammo (ammo quickly will become scarce) and Whoa, game paused and you offered to pay just 1$ for XX more bullets. Or you can just go and die (in game).
This situation looks absurd, but its pretty usual thing for mobile games...
Previously we was protected from this because its awfully hard to tie game with customer wallet - who will input card number in game? who will give that info to game developer?
But now...i just wait for surge of microstansactions on PC too (and i heard there is some first signs).
And that is just one possible bad scenario.

and it has absolutely nothing to do with Steam/Valve :)

Heh, you can say same that Android games in-apps have nothing to do with Google...except that Google Play absolutely allow such things.
Lets see that will be once Steam\Valve allow that.Until that, just enjoy games.
P.S. absolutely recommend to read about new "Dungeon Keeper remake for mobiles" and how "greedy" its become.

Oh, I know all about microtransactions, don't you worry. But since you mention the Dungeon Keeper remake - it is not doing very well at all... Just because people can do this, do not mean it will be successful.

Wrappers. They either make changes to the executable (for instance they did in case of Messiah, another 2000 game with CD audio) or put a custom DLL in a game's folder (similarly to how nGlide works, although I don't know whether GOG does that for CD audio). Basically the idea is that the game calls the CD audio functions as always but either whatever contains these functions was altered/replaced or something intercepts those calls. So the same function or function call that originally made the optical drive play a certain audio track may now make an audio library play a compressed file, or play the audio tracks of a CD-ROM image file etc..

And yeah, GOG pretty much always thinks of that stuff (I think the only GOG release that for some reason didn't play audio tracks as it should was The Nations but that may have been taken care of by now) unlike publishers who are themselves fully responsible for their vintage releases and usually ignorant of the existence of CD audio (or at least too lazy to make the games play audio files instead).

Actually indie games were among the first third party games to ever be released on Steam (like Darwinia or Rag Doll Kung Fu).