You can also buy universal rubber slip ons for the stands so there's more contact friction and not metal on metal. There's flat surface and there's ones that require the use of a slit stand. They sell rubbers for those, too. A set of rubbers should last a few years depending on how often you jack things up and the storage environment.
I'd be extremely uncomfortable with rubber on top of my jack stands. I want a well-formed saddle and I want them in a place of the car where they can make firm contact.
Metal on metal isn't going anywhere with the weight of a car resting on it-I don't want a rubber pad that the car can slip and slide around on.
I don't EVER recall seeing stands with rubber pads in use in a garage.
The shop building my MGA works on a lot of high dollar muscle cars and other collectible cars, and their jack stands are a lot mangier looking than my personal ones. They care more about the cars being secure than having pretty or fancy stands.