I've noticed the same thing. I guess the expected cable to use is the custom designed FPC (Flexible Printed Circuit) for the Novena LVDS interface, rather than generic FFC (Flexible Flat Cable). Custom flex PCBs seem pretty common for modern LCDs.
To test my "Novepad" adapter board prototype I got a generic 50 pin FFC from taobao (the same are on ebay, I think). The endmost 4 pins of the 54 are just used for the resistive touchscreen signals, so as long as you place the 50 pin cable at the right end then all the important signals should still be connected. You can kind of see this in the photos on the "iPad 3" thread.
There is a chance that the generic FFC won't be good enough as all the conductors are the same width & spacing. There could be signal integrity problems with the LVDS pairs or current draw problems with the power pins. The Novena LVDS FPC has routed pairs for each LVDS signal, and thick copper sections for power/ground. I'm hoping that with a short cable things will still be OK, though.