edit - georgemcbay points out that XCode is free. My mistake.
Unless you're willing to enter the grey world of hackintoshing, you need a Mac to develop for iOS (required for code signing step) regardless of how you build your app, even if you use a third-party compiler like the MonoTouch one.
I guess at least if you own a Mac, you're allowed to run Windows on the hardware as well. The same can't be said in reverse, due to software licensing restrictions.
My criticism of having to buy a Mac and use XCode to make an iOS app is in response to the criticism of having to use Windows and Visual Studio to make a Windows RT app. It's the same process. The only difference between Windows RT and iOS is that Microsoft lets you install Windows RT apps on a desktop/laptop as well as a tablet. Microsoft is far from pioneering this requirement by several years and half-a-million apps. Yet people are pushing this like it's a brand new Microsoft innovation.