groze: Well, GOG just released their version of Double Fine's Brütal Legend, which lacks online because the online on that game is provided via some sort of DRM (that's what I make of GOG's statement, I may be wrong).
EA and Ubisoft and whatever studio/company that requires DRM in order to play online could just release a DRM-free version on GOG just by removing the online features altogether. If a certain game relies solely on online play and the solo campaign or local multiplayer are the "extras" and are not full fledged, then I guess there's no point in having a GOG version, but if a game has a solid single player campaign and the online is just the extra, I don't see why they can't just do what Double Fine did. Do a lot of people want to buy Assassin's Creed 2 for its online offerings? This is a legitimate and honest question
I personally would be fine buying GOG versions of games with multiplayer part disabled, even though there seemed to be big arguments about Brutal Legend that GOG shouldn't sell it at all, if the multiplayer part is missing. Hence, I bought Brutal Legend from GOG too.
It is not an easy question though, and I guess that's why GOG was also asking in a survey whether people would be fine if the multiplayer part for some GOG games required a key/authentication to some other service. I personally would be fine with that as well, as long as the single-player part is still fully DRM-free.
Heck, in fact I repeat what I said here already like two years ago or so: I would be fine even if the games (new AAA titles mainly) that GOG sells would at first have online authentication DRM even for single-player, but there would be some kind of guarantee that the DRM will be removed after some time, say after a few months, or a year, when the game is not considered selling like hotcakes anymore.
I would be fine with a setup like that, as long as I knew when the DRM will be removed, and I can trust it. No empty promises like "Sure, we will remove DRM from all our games
if it ever becomes a problem.", but a more systematic way that it will get removed after some time, either way.