There's nothing to compare in my opinion. That's the Apple's policy regarding iPhones - they jut don't want you to buy contract-free iPhone. Of course they give you that option, but for the very high cost, which is unnacaptable for most people, that's why they opt for contract version - probably it's more money for Apple in the long term from AT&T and other carriers.Most iPhones are sold subsidized. I'm talking about unsubsidized iPhones vs unsubsidized iPod touches.
And one more thing - people do whine about US iPhone and iPod touch prices, but forget the fact Apple devices are way more expensive in other countries. For example in Poland iPod touch 8gb cost 345$, 32gb cost 460$ and 64gb cost 615$! iPhone4 16gb model without a contract can be yours for 1335$! So compared to that and most other countries, US prices are a bargain, and ppl still whine about them. I dream for US Apple prices here in Poland where I live.