Apple doesn't do that. The restrictions Apple impose are on distribution(i.e. you can't use Apple's distribution services to distribute your app to the users of that service if Apple don't let you), you can do whatever you like to your own device and Apple can't do anything about it. That's why it's perfectly legal to jailbreak your phone.
That's splitting hairs. They do do that, exactly by imposing restrictions on distribution.
Your argument is: "You're free to write an app for yourself, but Apple isn't restricting you from using private APIs, they're restricting you from distributing it using their resources, oh and they're blocking any alternative distribution methods, too."
