Valve aren't trying to make a business out of selling to Linux gamers. But Linux gamers are free, enthusiastic beta testers and bug hunters for Valve's console. I imagine most Linux using gamers already have some of Valve's games on Windows, and that Valve will throw in Linux ports as they did for the Mac. So there really cannot be many new sales there. But for beta testing, long time Linux users will do great QA, and Valve's console is their big ticket out of vendor dependence.