Was talking to a friend today bout the ps3 and he came up with this. its just a idea so here it goes.
Take apart the SDK model, take high resolution photos of the Logicboard. Work out what all the IC,s are.. Its possible that sony has put a extra IC on the SDK models, that retail consoles dont have. which the firmware that the SDK models run checks for. It may be simple to solder a chips to the retail console.
Hope i can get some light on this..