> Apple's own software almost certainly uses different APIs than what they force developer apps to use.

I think it's foolish to think that Apple uses private frameworks for their apps exclusively, when they could be using the public frameworks that other 3rd party apps use.

It's more likely to be: Apple uses the public frameworks for the majority of their apps but use the private frameworks for controlling the underlying hardware and subsystems of the OS [stuff like communications which could cost the user money, SMS, phone calls].