it may not be easy, but with the progress made by other game engines in last few months, running your game on linux is now a reality and as easy as making it for PC (with little effort).
It sure is, I'm a Linux-exclusive gamer ever since Steam on Linux came out, but I try to look realistically at reasoning of developers who never did this before.
But then "Windows PC" would be the correct term. "Windows OS" would imply that it also runs on e.g. Windows Phone, which is usually treated separately.
