Linux is (mostly) secure by design. How does Windows stack up?
Linux has a powerful command line interface which can do almost anything that can physically be done on a Linux system.
Linux comes equipped with programming support (I think a C compiler should be considered a standard part of ANY system).
Linux (generally) has resizable dialog boxes. The Windows environment variables dialog box is downright evil.
Linux allows for a great deal more system and desktop customization.
If you get used to running Linux, you can pretty much dual-boot or straight up change your OS on a whim (especially given the available of Gnome and KDE). Also, you have something to change to. If you decide you get sick of Windows, it's a much bigger deal to change OS. Windows to Linux is nothing like Ubuntu to Arch.
Installing and running a development/test web server on a Linux machine is almost trivial.
I would say in general where Linux excels, it excels far more than Windows does where Windows excels. Windows may be a little better in some areas, but where Linux is better, it's so many lightyears ahead that Windows isn't even in view anymore (think virus protection for example).