Depends on the choices you make architecturally. If your game uses libraries available cross-platform (i.e., Windows, Mac OS X, GNU/Linux (and thus SteamOS), bu

Depends on the choices you make architecturally. If your game uses libraries available cross-platform (i.e., Windows, Mac OS X, GNU/Linux (and thus SteamOS), but optionally also Android and IOS for games suitable for mobile) and your software build doesn't make any hard OS-choices, making your game available on each platform capable of supporting your game is almost always profitable, because the overhead is mostly taken care of by the libraries used, and what remains (some development, quality assurance, support) is easily covered by the added sales. If on the other hand you use libraries or in-house code that is not that portable, the profitability of making your game available on other OS'es is a matter of a couple of factors. Is the game good enough to garner enough sales to cover porting? Is the market saturated or is the game rather unique on the target platform? Does the game have lasting appeal so it can sell for years? How much will porting cost? These questions are not unique to Linux, this holds true for Mac OS X as well. There are benefits to having your game on Linux too; because there are less games available on the whole (although I am not complaining as an avid gamer on Linux) the market is less saturated than on Windows. So depending on the genre you are publishing in and the quality of the game, you may very well sell more copies per capita than on Windows.