Indie developers really get the dick on that score. I know Monday Night Combat is coming to PC at least half because their balance patches, essential in an online shooter, were going for months without being released because they're at the back of some fucking certification line, with big developers cutting in front of them all the time. It's bullshit and everyone smells it. Meanwhile, over on Steam, you push a patch and it goes live that day. Now, Valve isn't going to stop you from breaking your own game, but by all accounts neither is Microsoft, and at least Valve is prompt about it.
I don't think Valve is specifically trying to put pressure on Microsoft though, because this is stuff they've been talking about since Steam was first discussed openly in, like, 2001, and of course Steam launched in 2004, before the 360 came out. They're not out for Microsoft, they're out to change the way games are distributed and supported, period.