Because of costs. The Atom chipsets don't support USB 3.0 natively. So vendors would have to add NEC/VIA chips to offer USB 3.0. And since Chromebooks will be mostly working with WiFi, it won't matter much.
Cr-48 already reads SD and MicroSD cards as well as USB thumb drives. Various users have connected USB mice & keyboards to their Cr-48s. Printers (due to the nearly infinite number of drivers) currently rely on "cloud print technology."Will there be USB Chrome software support for, say, a data stick or an external mouse or a printer?
Connect a printer to Google Cloud Printwhat is "cloud print technology"?
according to Google Cloud Print Helpwhat is "cloud print technology"?