That's a load. I've been hearing this same thing for years now. More than half the Web Servers on the Internet are Apache. Apache, has source code, and, most Web Servers today, are an Open Source version of Unix. Windows is only the big boy on Desktops. In the Server World though, Unix is still the top dog. So saying that no one writes **** for those OSs because they have no user base, is not only incorrect, it's almost laughable when you consider that if you REALLY want to target the best potential out there, Servers are WAY more lucrative than Desktops, and yet it still doesn't happen.
And as noted, Linux, because of the small percentage of users, is not targeted light Windows and now Apple.