According to the svn logs, this feature was removed in r20911, because some operating systems didn't play nicely with this feature (mainly Windows I think). Evidently, this feature is still mentioned in the manual, but I think it should be removed, unless someone else knows a reason for it to stay or has any other comments on the subject.
USB charging can still be done, though, by holding the Select button while plugging in the usb cable to the computer.