teceem: GOG doesn't guarantee
future compatibility. Nobody does! The key word here is "future". Guaranteeing that something will happen in the future is fantasy/science fiction.
Eh? Guarantees are all about making a promise (or contract) that places liability on the on the guarantor. Nobody can predict the future accurately, so by that token, guarantees should not exist. Yet they do.
It's like warranty and insurance: death insurance doesn't prevent you from dying, but at least someone's going to get something out of it. Warranty doesn't prevent an item form breaking, but at least someone's taking responsibility for repairing or replacing or refunding the item. A guarantee is basically just a free-form warranty-like contract that covers arbitrary promises that go beyond "if it breaks, we'll make up for it somehow."
Understandably tech companies that deal in commodity consumer products don't want to take on such a liability, although it might not be as expensive as you might think. (How much can you claim in damages over not being able to play a videogame you got for a few bucks?)
That is, by the way, part of the reason our supermarket shelves are stuffed with cheap plastic shit that breaks and breaks and breaks. Yes, someone's responsible for the warranty, but as long as they can just keep replacing the shit with another cheap shit or say "okay, fine, have your three pennies back", there's very little incentive to produce a quality item that lasts. Taking them to court and claiming damages would almost definitely be far too expensive to be worth it, if the court doesn't laugh you out. A class action suit could work but these take a lot of effort to organize and require a large enough riled up population.. usually people don't get that riled up unless it's an expensive item they're having difficulty with.