Did it ever occur to you that Americans who travel or work outside of the States might want to use their unlocked GSM phones on international GSM networks by switching SIM cards? If someone who has fulfilled their contract with AT&T wants to travel to Europe and use their iPhone over there, they can't because Apple stupidly refuses to unlock a phone they've fully paid for. Your line of thinking is extremely small and limited. As I said, there's a whole world outside of AT&T and T-Mobile.
And just because you have no desire to use T-Mobile's EDGE network doesn't mean that others feel the same way. They have another carrier that is an option, but Apple & AT&T won't allow customers to use that option, despite the fact that their contracts have already been fulfilled.
It is actuallly a lot worse.
When I'm travelling abroad I like to use a local SIM to get a better rate.
However, once I fulfilled the contractual obligations with a subsidized iPhone, I also don't appreciate that AT&t requires a data plan for my iPhones even if I never use their data plan. I was willing to sign over my Family Plan over to AT&T but they insisted that any "Smart Phone" needed to subscribe to a Data Plan even if it would never be used on these phones. I consider this extortion. So you cannot get a regular voice only plan on an older iPhone???