Do those ads at all block/interfere with my ability to ride the bus/train? Do they use up (steal) my (artificially) limited public transit mileage (bandwidth/data-cap)? Do those ads track my bus/train trip and sell that info to other transit businesses? There's a pretty significant difference between those passive ads one sees (or ignores) on a bus or train and the sort of constant abusive behaviors we see from Internet advertisers.