Yes, governments can require interoperability and can limit monopolies. That's how antitrust laws work, like it or not. But if you want to get all libertarian, why should companies be able to use government power (as in courts, DMCA and the like) to shut down smaller companies that reverse-engineer their protocols?
I'm a major libertarian, and you have a great point. Apple should maintain their competitive advantage via technical means or let more cooks in the kitchen.
