[eyko]

OS X provides a user friendly interface on top of a unix like system. It's easy to develop for linux and unix-like systems in general on OS X. Not so much on Windows. Also, we like bash/zsh, and PowerShell doesn't appeal to many of us. Many of us also don't see much of a difference between running a Linux distribution and running OS X, other than the desktop user interface. The differences in the underlying layer get blurry. With Windows, no.

[guardian5x]

PowerShell isn't the only option available for Windows. You can install Cygwin or other alternatives and have your bash and linux-y environment on Windows.

[beagle3]

True. But if you spend most of your time in and around cygwin, it makes sense to switch to some kind of Unix -- while cygwin is marvelous, the nearly perfect Posix layer comes with a non-trivial performance cost - e.g., fork() is horribly slow in cygwin, as are many forms of I/O.