EDIT: By analogy, it's very like software portability. If you make your software support Windows and MacOS and assorted Linux distros and the major BSDs and Haiku, you'll get more users. But if you only target Windows you'll get 80% of the market, and Windows+MacOS will get you 90%, and after that you really need to think about whether it's a good investment to target more platforms. By all means, be accessible because it's the right thing to do or legally required, but it's not obvious that it's a sound business move.