I came across a page describing an issue with the Windows 7 SP1 update related to USB drivers
Seems the SP1 doesn't upgrade all the USB files correctly.
Microsoft released a patch to update the USB drivers properly: Binary files in some USB drivers are not updated after you install Windows 7 SP1 or Windows Server 2008 R2 SP1
Maybe the broken SP1 update caused you USB driver
to go into legacy mode (USB1.1)
I ran the patch myself and my "Windows\System32\drivers\usbport.sys" went from version "6.7.7600.16358" to "..16788".
Unfortunately it didn't fix my issue with virtualbox (unrelated to you prob)