The basic premise is that Apple wish to tie their OS to Apple controlled hardware. Microsoft don't give a hoot about where their software is running as long as they have their licence fee. Apple get pissed if you run their OS on anything but their systems.
They both have their business models, they both adapt their licence agreements to suit their models.
What that has done it setup a situation where you own a Mac, you're able to get the best of both the Apple OSX and Windows environments (and whatever else you want, provided you have a licence). On the other hand if you run MS, you're not legally able to run OSX even through virtualization as you are not able to purchase the OS independent of the Hardware. (if I am wrong on this second count, then, yeah, OK, I'll admit, I missed something)
Apple are playing this to their advantage which does not create a level playing field. This is not in the spirit of fair competition.