Making a SteamOS / Debian / Ubuntu version is not a so hard if they have an OpenGL output. They can use Mono for the Launcher and probably the user interface.
About support... It's a joke ! Just look at Steam forums : Community does all the job before companies even know there is a problem

For Yoshida-san :
Please, Yoshida-san, think about it : you could even sell incredibly powerfull customised Final Fantasy steam machines ! Unike old plateforms, it's a freely licensable operating system !

Just look at this (if it's not displayed in japanese, look at the "language" button on top-right :
http://store.steampowered.com/livingroom/SteamOS/

And you must know one thing : Gnu/Linux systems users Don't spend money in OS, but we can spend a lot of money into video games. Look at steam. A few users, but good customers.