When they pulled the "games for windows live only runs on Vista" back when Vista was fresh, it just made me not buy those games until there came out a worthwhile OS. There's too many old, great games I haven't played that won't require the new DX.
Also, do I know Valve right, they'll probably make sure games on their platform still runs on W7. GOG will probably do the same. And, seriously, any release that's not being released by Microsoft will run on W7 (and probably also XP), as the other big publishers has no gain from forcing people to use 8. This isn't a problem unless you really want to play the latest bad port of an xbox-game.
Case in point - I've been playing both Civ5 and Shogun 2 lately, and both can be played both with DirectX 9 and with 10/11, to ensure that both xp and Vista/7-users can play.