As has been said, the rubber pads were not a factory item; they were offered as an accessory, to be put on buy the owner. They do offer quite a bit more 'grab' to the pedal surface, which helps with control of the pedal.
A side benefit is that they protect the metal from wear. And for those who have old original petals, worn smooth by 50 years of wear, the rubber pads both hide the worn pedals and provide renewed grabbing power for the bottom of the driver's shoe.