Sooner or later the USB 2.0 ports on every Mac will be upgraded to USB 3.0, because its nature. They cant stay with USB 2.0 for the next 10 years, for example. Printers and small drives and other devices will use USB 3.0. Apple knows they will have to add them because if they dont MANY MANY people wont buy Macs, because it could be difficult to find thunderbolt devices or because most of their devices already use USB 3.0.