Former Valve employees started CastAR is what I was led to believe. From Valve point of view supporting CastAR is a good option because they want both initiatives to succeed (Oculus Rift is already supported in SDK). Why? More VR = more games, more games = Steam is more relevant. And with Micro Transactions (No other game distribution platform does it AFAIK. So if your game wants to use them Valve will take a cut.) Valve's margins and market segment is so high that investing in technologies like that (Steam Box/VR) makes sense even if they do not pay off for years. Eventually they will bring more people into gaming and Valve will be right there conveniently offering all the games that support VR right on the front page.