http://www.vg247.com/2012/03/05/valve-patent-shows-steam-box...
Remember that the idea of Steam on Linux was itself just a rumour mere months ago.
Regards the "Linux users pay more" meme on the humble bundle, bear in mind you are still talking about people only paying something like $10 for about 5 games. I assume that Steam prices will stay the same across OSs as well rather than charging more for a Linux version.
It's obvious that they are getting more interested in hardware such as the Oculus Rift, also with hardware getting cheaper there seems to be a growing market for people buying hardware/software integrated solutions.
Whatever it is they are planning to do, they want to become a first class player in the gaming market rather than being whim to Microsoft who look like they are wanting to produce their own hardware.
The best way to do that is to take an already proven kernel with good performance and no licensing and work on from there.
My guess is that porting Steam to Linux gives them an eager powerbase of vocal power users to use as a test market. It's the same principle Apple uses by marketing to the "fanboys" first and letting it trickle out from there.
Hopefully they will continue to support "normal" Linux distributions however, it would be nice to be able to hook up their controller and a headset to my PC and run everything that way if I don't want to buy a "steambox" or whatever.