Requiring a minimum purchase seems silly to me. Having the iPhone set up with an exclusive carrier made since until the 2nd iPhone was released. After that, it is just a douche move by a major corporation. Apple should really drop the minimum purchase requirement and allow the iPhone on all carriers as long as the current hardware supports said carrier. What would the harm be in doing that?
I believe Apple has good reason for this. Here is why:
My girlfriend works at Planet Cellular which is phone store mostly located in the southern US. They sell phones for the AT&T network. The corporate company has told their sales people not to sell over 30% iPhones. Corporate doesn't want them to sell too many iPhones because of the large subsidy of the device compared to Android devices.
Also, the individual sales people, aka my girlfriend, work on a partial commission. When they sell other phones, aside from iPhones, they earn more GP which is the total amount of sales that their commission is based on.
Basically I believe that the minimum requirement may be Apples way of fighting back against major incentive for carriers and sales people to sell less of the iPhone and promote other brands.
People have to understand that the average consumer doesn't know what most people on these forums knows about cell phones. Everyone here may go into a store and know exactly what they want. The old women and men going into my girlfriends store can be sold on almost anything. Planet Cellular is just my own personal example of a store that I know is leading people away from iPhones.