They don't ban them just to ban them. There is a list of things you can do on the phone. It's the approved public API. Stuff that does things calling other fun

They don't ban them just to ban them. There is a list of things you can do on the phone. It's the approved public API. Stuff that does things calling other functions are banned. Things that change how the device behaves in an unpredictable manner are rejected out of course. This makes it pretty foolproof to make apps not hurt other apps. This is a feature that makes iPhones tons easier for your mom to use (and to freely install apps on) than Android phones. Lots of these things that use non-public functions are detected with a scanner that looks for calls to non-public functions. For the camera functionality in particular, they were told to take it out, they did, but hid it in a secret portion of the app. Apple banned them for abuse there. For every neat app like Camera+, there are 35 utterly phone breaking apps out there that would do stuff like this. And it's not like those apps don't have a place to go. People who care (possibly you) often jailbreak and buy apps there.