But here is the thing if you ignore the technical stuff.
If a developer ignores Windows he will lose millions of potential sales, if he ignores Linux is will still sell as much because any potential buyer will have a Windows partition. Just look at the Mac and how it is a low priority for developers (not every company is Blizzard).
If Valve went and put Windows on the hardware with standard hardware then it will be a different story (and a much better product). However if they go with Linux and literately start from scratch (and NO having a Windows emulator doesn't count) because non of the games work properly the whole project will be a failure. How many of the games you currently own actually work on Linux....