But more importantly, he's responsible for iOS and the entire Walled Garden concept around and behind it.
You give Forstall too much credit. The nature of iOS and the 'walled garden' most likely came from Jobs, as most things did, and Forstall was just in charge of making it happen. He might have at most suggested the idea of vetting and approving apps but Jobs would still have had to sign off on it making it still ultimately his decision not Forstall's.