What is "enterprise" in this context? Do they work for an enterprise SaaS/vendor or for an actual enterprise, aka big businesses that use software? I don't think either of those are particularly better paid than the other groups.

I think it's more likely that the best paid programmers are working in a field with specialized software that only runs on Windows. For example, EEs use Windows almost universally for Altium/Cadence/Mentor Graphics software which means that the majority of commercial firmware compilers and IDEs are Windows only too (even though many are forks of cross platform tools). The same is pretty much true of biotech too: a majority of the software that interfaces with hardware, especially lab automation, is on Windows so anyone dealing with those specialized fields would be start with Windows and run VMs for everything else.

Another explanation would be hardware support. My workstation has a high end but not a server mobo (with funky features like Marvell's weird simulated RAID) and dual SLI K-series GPUs (professional/super computing). Getting Ubuntu 14.04 to even boot up, let alone properly deal with monitors and peripherals like a 3D mouse coming and going, takes at best an entire work day. Windows 7 with NVIDIA's drivers and VMWare leave much to be desired if you're a fan of Linux but they just work, especially if you have to do anything with CUDA at the same time as your main line of work.

Also: Visual Studio.