So much for all us geeks who like to play around with the hardware and learn things. If everything back in the day was as closed as Steve Jobs wants it to be now, do you think we geeks could have learned so much ourself? Just to code some simple hello world application you would have needed to buy a "coding" license from Apple. Not really feasible for a 10 year old kid who is just starting to learn programming.
You must be looking at how Apple controls mobile devices and not desktops. A license is not required to develop Mac software (or even iOS software as long as you don't intend deploy it to the device). To look at how Jobs controls access to mobile devices and to extend that same logic to the desktop is a little naive. A desktop computer that wasn't open to creating new content or building software etc. would be pretty useless and nobody would use it. Unlike mobile devices which really are for communicating and content consumption.
The bigger the theory the better.