.NET is massive. Just look for job listings. C# gets more money over here in the UK than C++, with there being far far far more jobs using C# and .NET.
Also, just look at how many developer jobs there are in Windows-land versus Linux-land: you hardly ever see Linux development jobs apart from embedded development. Windows is huge.
Good point! But the job descriptions will never specifically ask for strong Linux skills - they want you to code and upload, and the languages are not tied exclusively to Linux (although I don't know anyone running a real production server with PHP under Windows, so you're right!)
Also, just look at how many developer jobs there are in Windows-land versus Linux-land: you hardly ever see Linux development jobs apart from embedded development. Windows is huge.