Except that while Valve won't openly admit it no company goes in to the cost and time of developing a whole new OS without the intention of capturing a portion of a market share and thus the money that goes with it. While it is fantastic to think that Valve are being altruistic with it's Steam OS the reality is that they are aiming the OS at a market share that is currently the occupied by Sony and MS, a device that integrates in to the living room and can be used for multiple purposes; gaming, movies, music.It might help if people stopped assuming the purpose of the SteamMachines is for them to be "Playstation/Xbox/Wii" killers.
The more Steam OS they shift the more money they make through Steam store sales for addon products, at the moment that is gaming and the odd program but with film streaming services you can bet your ass that Steam will want a cut of anything that goes through their Steam service.
Where the Steam OS falls flat on it's face is with gaming exclusives, no one is going to develop a purely Linux based game, they will make a Windows build and then convert it and then you have the back catalogue issue. It's an OS that is built around Steam ergo the assumption is that you're current Steam account plus all it's games should work on it except that they won't, you'll either need someone to convert them (none of the big publishers will waste the time or cash on that) or you need a second PC running Windows from which to stream the games. An issue that neither the XBone or the PS4 suffers from.
Valve aren't doing this for the good of the gaming world, they are doing it for cash plain and simple but so far the news they have announced is less than stellar. If you ever wanted proof of this concept take a look at the next big name title that Valve release, I bet my arse that it will be available for both Windows PC as well as Steam OS.