This is also why I see Sony having great success with its Morpheus headset. The PS4 is cheap as-is ($399) and if you already own one, its a no-brainer to go with their product. I'd be really surprised if Oculus ever goes mainstream. It still looks like an uber-nerds hobbyist toy like a, say, 3D printer, which technophiles have been telling us for years would be mainstream by now and in "every kitchen."
Carmack isn't stupid. He didn't sell to Zuck because he thought he'd be moving 10's of millions of product every year. He sold to Zuck because he knew that the shipping date doesn't really change things for Oculus. Its still a very rough road to mainstream acceptance and economic competitiveness. I can afford $299 for the headset, but I'm not interested in buying a super gaming box to make it work. Nor am I interested in being a beta tester for a technology known to be a bit wonky, cause motion sickness, have questionable 3rd party support, and Facebook ownership/integration/driver and API's TOS.
This is what on top of what Valve is doing, which may just steal Carmack's thunder as they have everything they need to make this work: the store, no relationship with unrelated businesses like social networking, large customer base, community goodwill, game publisher relationships, a decade plus in the game selling world, etc. If both the Valve set and the Oculus set go for $299, I can't think of any reason to even consider the Oculus.