This is an outlier, since the Windows stack is so closed in general. I think a large number of VS users use it because they are forced to by their environment choice (or employer).
I tend to think of editors like TextMate, emacs, and vim to be chosen by people who invest some thought into making the decision, rather than by people that are forced to use something for work.
Perhaps it's an outlier in that the language is more closed than most (and that this gives MS a pretty huge advantage over other IDE makers), but VS really is the best environment for developing .NET. That's why people pay for it, not because management forced it on them.
I tend to think of editors like TextMate, emacs, and vim to be chosen by people who invest some thought into making the decision, rather than by people that are forced to use something for work.