am i missing something here?
From a Google search: Something to do with mega-bytes per second as compared to mega-bits per second. Not the same unit of measure.
And here is a fact sheet about USB3 for you to read.
____________________________
4. How fast is USB 2.0?
USB 2.0 has a raw data rate at 480Mbps, and it is rated 40 times faster
than its predecessor interface, USB 1.1, which tops at 12Mbps.
Originally, USB 2.0 was intended to go only as fast as 240Mbps, but in
October 1999, USB 2.0 Promoter Group pumped up the speed to 480Mbps.
As far as we know, effective rate reaches at 40MBps or 320Mbps for bulk
transfer on a USB 2.0 hard drive with no one else is sharing the bus. Flash Drives
seem to be catching up too with the some hitting 30MB/s milestone. For
all we know, USB interface could become become the bottleneck for flash
drives as early as 2008.
Additional notes from Alex Esquenet - our engineer friend based in
Belgium: "A fast usb host can achieve 40 MBytes/sec. The theorical 60
MB/sec cannot be achieved, because of the margin taken between the sof's
(125 us), so if a packet cannot take place before the sof, the packet
will be rescheduled after the next sof. On top of that, all the USB
transactions are handled by software on the PC. For instance, a USB host
on a PCI bus will send or receive the data via the PCI bus; the stack
will prepare the next data in memory and receive interrupt from the
host."
