Microsoft Windows programmers do have an option here, with the ability to acquire a Mac box (which has prices that are analogous to similar-quality Windows hardware from reputable Windows system hardware vendors) and can then load and run and can choose to develop for Microsoft Windows, Linux, BSD and OS X. On the same (and good-quality) box. These other operating systems can run directly on the hardware with Boot Camp, or can run as guests in one of the various available virtual machines. And you can develop iOS from this configuration.
In general, developing applications for OS X is very different than developing applications for Microsoft Windows. Given what I've seen of Microsoft Visual Studio and the various Windows APIs over the years and what I know of Xcode and Objective C and Cocoa, I'd have to assume there are very few people that are particularly good at programming on both platforms. (I'm sure there are at least a few, but maintaining skills on both platforms is a large(r) effort given Apple's 10.7 Lion and upcoming Mountain Lion and Microsoft's Windows 7 and upcoming Windows 8 releases.)
As for OS X or any other operating system running on non-vendor-provided platforms, supporting arbitrary hardware configurations is massively expensive. There are differences among the hardware and driver-level interfaces within USB devices, and variations among pretty much any other category of gear on the market. Often substantial differences. And there's little or no revenue returned from that effort.
That Microsoft and the various vendors that are selling systems and peripherals for Windows do as well as they do with the massive range of hardware that's available for Windows is still (to me) an impressive achievement. Microsoft is staggeringly good at keeping the vast majority of that hardware and software stuff working, and across comparatively massive upgrades. It's not easy to maintain such a complex installed base of hardware and software; not by any stretch. And it's not cheap for Microsoft to maintain all that testing and all that compatibility.
If your quest here is simply for OS X on cheap(er) system hardware, Apple was in that market back in the 1990s. It didn't end well.