This would be resource sink for reasons outlined by my sister comments. Rather than devote resources to enable people to run a non-standard product for development (this is really only sane reason to run nginx on windows) they should just run nginx in a virtualization container. VMWare Player is fast and free. No work has to be done to support this use case.
Too much wasted effort is put into open source projects to support windows. This is isn't about not supporting Windows because of MS. But by not being Unix, it causes too much perturbation for little gain that can achieve through more correct methods (virtualization).
There are also deep cultural differences between Unix and Windows; how many people want to straddle both worlds? If you actually like Windows, wouldn't you want software that's Windows-like instead of stuff ported from Unix? The community is probably big enough now to support a Windows-specific open-source Web server.
And that server is not nginx. It is designed for Unix, it isn't designed for windows. The current apache has an arch much more amenable to running on windows.
Too much wasted effort is put into open source projects to support windows. This is isn't about not supporting Windows because of MS. But by not being Unix, it causes too much perturbation for little gain that can achieve through more correct methods (virtualization).