That's the Canadian store. You can't get them on the US site.
I just checked and it looks like you can... 699+
Go to the US site:»store.apple.com/us/browse/home/s···/iphone5
I was just there and saw unlocked, now I don't. Maybe it was the Canadian site I was on but since I typed apple.com not sure how I would have gone to Canadian site.
It probably was the Canadian site somehow. The US unlocked iPhones have gone for the same as the contract-free phones, which start at $649.