tfishell: In theory, if a game is majority single-player, devs can wait until all major patches are finished / major bugs squashed, then throw the game up on GOG. It's far from ideal but that's better than second-class treatment. (I care about important bugfixes but not really client features, so - personally - missing achievements or multiplayer isn't necessarily "second-class"
to me/my purchasing decisions, but I understand not everyone feels the same)
From where I'm standing, only getting a game after it has ceased development is the right way to go, and that ensures no future missing patches. (And of course, being firmly against a client, features that require it aren't even irrelevant, they're harmful in my eyes.)
That still won't take care of the situations where you have missing Linux (or Mac) versions or missing content freely available elsewhere though. But would sort out most major stuff.
... Except in case of the devs who mainly look to maximize profits of course, like the above case, since most of those tend to be shortly after release. But those aren't, or shouldn't be, worth bothering with in the first place.