The apps store is optional and is almost entirely for the tablet apps that are largely for RT which is basically windows8 lite, I don't think MS is stupid enough to attempt at locking down the OS.
And as for valve, Gabe has his own agenda to bring Linux to the mainstream, so he is huffing and puffing about things that don't actually exist to serve his own love of Linux. I haven't heard anything from anyone in development other than Gabe, and seeing as everything from windows 7 runs fine on 8 I don't see why they'd have any issues.
Yes, the performance increases are small, on higher end equipment, but the OS is not really a factor if you're speaking solely about top of the line hardware.
Just remember, people lost their **** when windows implemented the start menu, now they are doing it again because it has become a start screen... It's not really that serious.