I don't know a single person that uses windows for development other than people writing windows specific(.net) software, judging by the overall vibe on HN and /r/programming I'd assume this is a general trend.
It's really easy to get caught up in the SV culture, but it's by no means the rule. There's millions of developers out there whose code is never made public, writing Java, .NET, C, C++, Ada, Fortran, and other languages that HN would regard as obscure, niche, or dead. They're consulting or working for small businesses, medium size businesses, enterprises, local, state, federal governments.
I don't know if most of them use Windows, but it's definitely a hugely substantial fraction. It's not a small minority.
Where I work, it's a 50/40/10% split between Windows, OS X and Linux as our DE's, though most of us run a Linux VM for the development server to run on. Makes life easier that way, and with Vagrant we're all running the exact same environment, despite differing opinions on how to do things!
If we had to target UNIX systems, the development was done via XWindows or telnet/ssh to common build servers.