MacBook Air USB Port is on Steroids

As a possible BTO with the MacBook Air, Apple offers an USB external DVD burner. This peripheral can NOT be used on other hardware, and this has nothing to do with some proprietary policies, but simply with its power requirements.
An optical drive drains a lot of energy, especially with CD and DVD burners when the laser beam is light on for several minutes at full power. The UJ-857 often found in Apple notebook officially requires 1.5A (and the reality is probably beyond).
It is a lot, and way too much for a single USB port (0.5A usually at most). So Apple decided to boost the power capacity available from the single MacBook Air USB port to make it compatible with the external SuperDrive. In addition, the MacBook Air could also be able to power any external 2.5" HD without the requirement of a dedicated power supply for the peripherals.