Whether he agrees/disagrees won't change the fact, which is, Steam runs on Windows 8 and it runs fine. There are a lot of reasons not to support an OS besides compatibility.

With Steam, it wasn't a compatibility issue, it was more to do with Valve feeling threatened by the Windows Store Model. Giving away X of every purchase to the store does undermine their profit model. The same reason why you won't see subscription based products such as Dropbox/Google Drive/Skydrive with upgrade options on the Apple Store.

However, I can't see how Windows 8 threatens the traditional form of sale, that download to desktop and play.

The fact the Gabe was attacking W8 is because of Metro, not Windows 8 itself. I blame the sensationalist media from manipulating it into what it became.

The real threat is Metro, not Windows 8. It is the anti-freedom, walled garden that everyone should fear.