Soldato
Because changing a device that costs hundreds and throwing away all your apps, is really a free market
There is no direct competition between them, if you own an iphone you can hardly use the Microsoft store.
As I said above, I can't use OS X applications on Windows and vice versa. That doesn't mean it's a monopoly. The same applies to smartphones.
People change their phones all they while. I've gone from an iPhone 4s to a Nexus 4 to both and iPhone 5 and Nexus 4.
What I do, and I suspect that people don't, is make sure my data is universally accessible. That way, changing from phone to phone is fairly easy. Yes I understand I won't be able to run iOS apps on Android but I understand I can't do that in the desktop world either.
None of this makes it a monopoly, locked in to some extent sure.