It takes care so it's only worth to make it portable between stuff that might give some money back (PS3, 360, and hopefully Win32). Linux lacks some important stuff too, such as a modern 3D API (using D3D gets you in Windows and the 360, and the PS3 doesn't exactly use OpenGL and for best performance it's recommended to access the hardware directly anyway so it's not like you've got the Linux version done for you)