Paper plates are still required. The number on it may not be as large as the actual plate, but there is definitely a unique number on it that is absolutely registered to owner of the car.
This sounds a lot like urban legend / internet lore
California did not require numbered paper plates when Jobs did this. Car dealers would put paper plates advertising themselves on the car, but you could remove them. Your temporary registration was taped on the inside of the front windshield.
I personally saw his SL500 with dealer plates a couple of times while visiting the Apple campus as a vendor. He'd park in the handicap spot too.
This sounds a lot like urban legend / internet lore