Well Valve can only promise this when it comes to their own games (HL3, Portal 3 and so on). When it comes to other publishers and developers they don't have much say other than "We think its a bad idea" so we can still see SteamOS exclusives.
All you need to do is release the game for Linux only. I highly doubt Ubi or EA would pull such a trick, but can see a Indie doing it easy.




