It IS the reason why apple features work as advertised more often than other manufacturer's solutions. Instead of trying to account for the myriad of devices out there, they just use devices that they have control over. If they make all the devices involved, they can do things on both ends to ensure painless operation. It's limiting to someone who is used to a more open system, but it's also a crucial part of their success. You can't do away with the "walled garden" while maintaining the positive aspects of that philosophy.
It's the same thing with requiring itunes to make changes to their devices. If you need itunes, that means you can't do anything to your phone that itunes won't let you do. If they limit what itunes will let you do to actions that can never screw up your phone, then you'll never screw up your phone. Most people will just remember their last iphone as a solid, non-glitchy, painless to use device, not necessarily realizing that it was apple limiting them to safe actions that made it that way more than anything else.