SteamOS might be able to optimize for the Oculus Rift in ways that Windows and Mac OS can't. I guess we'll see.
Also a new platform means reducing the value of software available to windows/mac, since everything needs rewriting.
Absolutely. I really disappointed by the lack of 4K in the Xbox One and PS4[1]. When blu-ray was new, it was the PS3 that really drove adoption. Now, the newer consoles will drastically lag behind the state of the art (compared to PCs), which will be exacerbated by the relatively long lifecycles of consoles.
I feel once consumers experience a VR demo in the next 2-3 years, and start seeing 4K games on PC (both perhaps as in-store demos), going back to their consoles is going to be very disappointing.
[1] http://reviews.cnet.com/8301-9020_7-57592390-222/why-next-ge...