There are a lot of people (myself included) who run both Windows and one or more flavors of "*nix". Frankly, the idea that I can't answer Linux-oriented questions from my Windows box because I'm using a Windows box is offensive to me.
I consider myself to be just as strong, if not stronger, in my knowledge of the plumbing of the operating system as well as many popular tools on GNU/Linux, both on the desktop and the server, as I am with Windows. That's because I've a wealth of experience and have worked on many, many different projects for many different people, who have different preferences when it comes to the choice of technologies (operating system being one of them).
Throughout the course of the day, I often sit at a computer running Mac OS X, Windows 10, and often even Ubuntu, for multiple hours each, per day. What influence does the system I'm currently using to answer questions have to do with the quality of my answers?
Lastly, you should know that it is laughably trivial to change the identity that the web browser presents to the web server. I could run Windows XP and make Super User's web server think I'm running Ubuntu 16.04. A website literally has no technical mechanism at all at its disposal to know that my web browser is lying about its identity or the operating system running it.
For more information about the mechanism by which web browsers "tell" a web server which web browser and OS they're running, read about the User-Agent HTTP header.
Here is a popular user agent switcher extension for Chrome, just as a proof of the concept. You can change the browser you expose, the OS, or both.