I am not sure I get the "no ID" angle. Maybe this will be the new phone of choice for terrorists. Anyway, you are only allowed one purchase per day. Since you don't have to give an ID though, the whole "one per day" limit is pretty meaningless.
Here is the catch though. The phone is still locked to AT&T's network. You are welcome to unlock it, but you are on your own with that task.
I am sure there are valid reasons for buying a phone like this. Giving it as a gift would make the most sense. If you already have an AT&T account and want to switch to the iPhone, this new policy makes it easy to walk into any Apple store and pick one up. I suspect for most of us though, buying it with a contract makes the most financial sense given the huge subsidies AT&T gives with a two year contract.