You are right that the OS and it's components are opensource and any changes made to them require to be open source. HOWEVER, if the game was made in Linux, SE would still own the rights to their code and could keep it closed source if they so choose. Programming on a particular OS does not mean you have to make it the same source material. If that was the case, then anything that runs on Windows, Microsoft could then take and use themselves.

Quote Originally Posted by indira View Post
snip