I really don't see why a MacPro or Macbook Pro 17 are in the least bit necessary for iOS development. Developing iOS apps really doesn't require that much power, just screen real estate if you are using Interface Builder. For iOS development, the 27" iMac or any one of the Macbook Pros or Airs paired with a 27" Thunderbolt display are more than adequate for the job.

FWIW I just sold my Macbook Pro 17 inch after my new job gave me a 13" Air. After using the Air, I can't even imagine lugging around 17" anymore. The convenience of the Air paired with a large external display when necessary is perfect.

The only professionals that have a legitimate complaint about the MacPros and Macbook Pro 17 are those doing a lot of intensive video and audio work.