If you look closely, you'll notice that the vast majority of the phones where the asking price is higher than retail are NOT selling. For the ones that are going for exorbitant prices, you can tell that there's a scammer artificially jacking up the prices. It's only the phones that have a low starting price that have a good number of people bidding on them, but even then, those prices are hovering between $500 and $600. Nobody is bidding beyond that point.
It's a simple matter of supply and demand. There is a ton of supply and not enough demand. Don't get me wrong, demand is high, but not to the point of selling out en masse like consoles. If there were none available in stores, then yes, the iPhone would be selling for ridiculous amounts on eBay. But the fact of the matter is that you can easily walk into most Apple/AT&T stores and just buy one without a problem. So it simply doesn't make sense to pay more than retail prices on eBay.
I feel really sorry for those people who bought a bunch with the intent to sell them online for profit. It's sad because they're actually losing money for setting the price so high and not getting any bidders at all, and for those people who are actually able to sell theirs, they're losing money because of eBay charges, not to mention the time spent waiting to get them. I know the people who do this sort of thing regularly didn't touch the iPhone because they knew that there would be plenty of stock. The amateurs got screwed big time