If a shop doesn't work with your browser/os you can buy from another one.
If your government web site doesn't work with your browser/os you've no other recourse, so the democratic imperative is to get rid of closed formats and browser/os specific public facing applications.
Then, and only then, everybody can use what he prefers,be it windows, linux, macos, bsd or whatever.
The problem is that they "democratically" decide that windows is on 90% of computers, if it works with windows is good enough.
Guess what? Things change. Just a few years ago internet explorer accounted for 99% of the market, and just a few were using alternative browsers (and facing the problems, I still remember many many sites not working with mozilla or simply refusing to be accessed from anything other than IE even if they worked properly), but now mozilla has a sizeable share of the market, in part thanks to those stubborn individuals that kept on using an alternative browser.
You aren't realy free to choose if one operating system is mandatory and we know pretty well that there's no technical reason for it being so, just some ***** that made some "strategic" undemocratic decision.