While it's true that Apple is getting paid smewhere, somehow; 'how' Apple is getting paid is completly different that the current manufacturer/carrier relationship. This makes all the difference as manufacturer is, for once, committed to making the best possible phone and isn't interested in coming out with new models at break-neck speeds to increase its profit margin.
But Apple is not getting paid installments for the cost of selling an iPhone. It's getting a payment for a portion of the subscription fees. This is not a subsidization of the iPhone as Apple is not getting paid a direct one-time fee for the sale of the hardware like with all other carrier/manufacturer relationships.
Of course it is, since the subscription fees is their bread and butter. But the reason for the payment is different. Apple is selling the hardware for little or no profit but will get it on the back end instead of up front.
Scenario 1: Customer purchases RZAR for $100 with 2 year contract. AT&T pays Motorola $300 for the sale. 3 months later the customer decides he doesn't like the phone and purchases a Nokia. Motorola already got it's money.
Scenario 2: Customer purchases iPHone for $500 with 2 year contract. AT&T pays Apple $500 for the sale. 3 months later the customer decides he doesn't like the phone and purchases a Nokia. Apple only gets 3 months of subscription based fees.
I don't see how not being able to go into an AT&T Mobility store to get service would benefit the consumer.