Valve is not big enough to take on Microsoft. Sure, they've gotten a lot of games to join their Steam Club, of late -- Dreamfall, Silverfall, Prey, Dark Messiah, and numerous others, but they are not a huge enough company or publisher to battle Microsoft.
The only thing Valve ever did was invent some l ½-baked online intrusive game service (STEAM) and tie it to their great Half-Life series.
Is Valve right about Microsoft? Yeah, well -- duh, Microsoft is trying to push "Vista," of course; its their new baby of an OS, so of course they'd push it! And Microsoft has been trying to put PC Games in the front-line for years. Finally, it seems Win XP really succeeded w/ PC gaming, more so than ever. There's a plethora of developers out there and plethora of great games already on Win XP that are really are doing the talking, if you ask me -- the plethora of games just being on Windows OS's are really making the mark here, not Microsoft's new campaign for Vista. Microsoft's campaign might try for Vista, in which might try to make things easier for PC gamers, but that campaign ain't going to take off on Vista until some of the kinks get worked out of Vista itself, in probably a few years or so. It don't help that they're OVERLY pushing it by pushing Halo 2 PC and Alan Wake as Vista exclusives is the first mistake; since the OS wasn't even out, yet they announced Vista exclusives. WTF is that??? Especially w/ Halo 2 PC, which is a port of an (original) X-Box game!!!
Plus, like y'all said, we all knew that years ago when it was "Longhorn" that Microsoft wanted to make PC Gaming more accessible as they stated so in interviews long ago, so why does Valve need to reiterate this to us? VALVE, we're not freakin' morons!!!