That is a great point.
There are almost always plusses and minuses in every design and decision, and forums like this allow for many people to point out possible pitfalls.
There are several things one should consider when deciding what type of floor to have. My primary reason for pulling up the carpets has to do with allergies. The previous owner had cats. My son starts sneezing and his eyes water when he is upstairs for more than 20 minutes. I mentioned "upstairs" because he used to have the allergy problems everywhere in the house, but when we removed the carpet in my man-cave, we discovered that my son has no allergic reactions there.
Yes, little rocks can get caught in tire tread, but I don't think that will be an issue in MY case for the following reasons:
In order to get into my house, I have to go a fair distance over clean smooth concrete, and in the rare occasion when I do pick up a pebble, I can almost always hear it clicking against the concrete.
I frequently inspect my chair for mechanical soundness, cleanliness, tire pressure, and tire tread condition. I have only found a pebble in the tread a couple times in several years.
I use tires with a tread pattern that does not seem to be prone to picking up pebbles. Its tread is not as deep as an off-road tread, and the tread grooves are narrower near the tire and wider at the surface, so the pebbles fall out easier.