Well, that's certainly an article title isn't it. But I mean it. Microsoft, don't you dare touch Valve. You're fat enough already and too big as it is.
Honestly I'm not sure - as I said I don't use it. I know of at least one game that's "DRM-free" but requires the GOG launcher for multiplayer (No Man's Sky). That's fairly controversial and I think the only reason why it's on GOG is because it came onto GOG back when it was a singleplayer only game.