from what ive learnt Moonlit is correct all the way, suposavly 'Memorex' have found it to be cheaper to just mass produce U3 tech, it is done this way so that 1 machine can make all flash drives, the difference is the storage chips, when they are being created they are either flashed with U3 image or a Non-U3 image, simply the Non-U3 sells for less, and is normaly a lower Capacity, the found one here being 32 meg (i think).
Though it seems not all Memorex flash drives units are produced in the same factory so only set models are U3 fakes.