Although we are a little bit late on this assessment of the two different USB types, we thought it would serve as a good reference point for our visitors.
USB 2.0 Vs. USB 3.0
USB Release Dates
USB 3.0 Backwards compatibility reference
Backwards compatibility: USB 3.0 cables have more contacts and components. Both the host (A) and the device (B) sockets have been deigned with the ability to accept USB 2.0 connections. At first site of the USB 3.0 version you most likely will think to yourself; "how can this fit"? but it does, thus allowing new USB 3.0 devices to accept USB 2.0 legacy cables.