Yes , but if you are not selling Linux, there is absolutely nothing to be gained from catering to that demographic (Unless they are actually not buying a game because they are thinking about switching to Linux and don't want another reason not to switch).
It's not like you have to pay some license fee to release your game on Windows
Thus all that makes sense it to cater to the existing Linux users (or those that have already decided to switch), and it can make sense to cater to a niche market if you expect it to grow in the long run, and by supporting them early you get a lot of loyal customers.
A big player like valve has little reason to do so however.