you get an OS that WORKS BETTER. Apparently there's an increasing number of people who think it's worth it.
Oh, and actually, Microsoft WAS hit with antitrust litigation over the whole IE monopoly they were working on. Apple's OS was written by Apple. Proprietary is NOT the same thing as monopoly.
If you want your hardware and software built by separate companies, you can. Even if it's crappy. Apple isn't stopping you.
". . . controlling all aspects of the market?" Seriously?