Certainly there's a correlation between operating time and total mileage. It's going to be different for city driving and highway driving but there's a relationship that holds for most normal use cases.

That said, there are specific costs that are primarily about distance (fuel, tires). Furthermore, probably overly conservative oil change recommendations notwithstanding, essentially all car makers express maintenance intervals in terms of mileage not hours (which could easily be measured). I'm inclined to give them the benefit of the doubt that they know what they're doing.