OK, so $27.45 * 24 months is $658.80, that's $109.80 more expensive than the unlocked iPhone by itself. AppleCare+ is included, that's $99, so that brings the leasing premium down to $10.80 over the course of two years in Apple's pocket for financing the hardware. And then, halfway through the 24-month financing period, you get an upgrade to the latest device. Sounds legit to me, and a much better deal than carriers are offering.
If you purchased outright each year, you'd spend $648 the first year, $648 the second year, but get back approx. $300 for selling your previous-gen iPhone, bringing the total hardware cost over 2 years to $996.
This program also puts a whole lot more power into the hands of the consumer, as they are unlocked and can be used on any network. If more and more people are using unlocked phones, we might actually see some real competition in the wireless industry when it comes to things like customer service.