I'm not sure that we can't say car ownership is a consequence of location. Plenty doesn't mean all, and transit access == zero vehicles is an argument no ones making.
Clearly if a household moves from several cars to one car, fixed costs will decrease, which seems like an argument to measure fixed costs.
I'd agree with your point about vehicles potentially being leisure expenses, you could perhaps go further and start dividing up those fixed costs between leisure use, and business use. I'd even accept the argument that if you need a car, your leisure transport should be free from the fixed costs, as they have to be borne anyway, but they do have to be accounted for somewhere.
Clearly if a household moves from several cars to one car, fixed costs will decrease, which seems like an argument to measure fixed costs.
I'd agree with your point about vehicles potentially being leisure expenses, you could perhaps go further and start dividing up those fixed costs between leisure use, and business use. I'd even accept the argument that if you need a car, your leisure transport should be free from the fixed costs, as they have to be borne anyway, but they do have to be accounted for somewhere.