No one does that, it is a HUGE rip off.
Better for the carriers to take the hit rather than the person.
People in Europe do that (pay full price) more often and T-mobile charges less per month if you don't buy a subsidized phone (except that promo they're running right now) so no contract works for me. The other carriers make it so there is no incentive to buy the phone outright. The service costs the same; only difference is the ability to drop them if you don't like them. I finally dumped AT&T for T-Mobile and while I wish they had the iPhone it's not worth it to me.
I prefer owning the device and getting less expensive service. I DO NOT want that AT&T merger to go through ever!
Cheers,