i don't think this rumour is going to be correct at all... apple "license" all devices that are made for the ipod iphones, and ipads by using the dock connector as the interface (the dock connector is what companies need to pay a license fee to use). if they turned over to standard usb, there would go all the license fees, anybody could make a device for an i whatever without paying apple a single penny..
also, the ipods, iphones ipads conform with the "must be able to charge from a standard usb port" ruling because they all ship with the cable that runs from the dock connector to a standard usb port.. this enables the user to use ANY usb charging device (plug in wall, or computer usb port) as the dock cable provides the link and is included with the device when purchased.
so i don't think the usb port will appear anytime soon, if ever....!