I'd expect most affluent households in most metro areas (chunks of NYC being the big exception) to own a car. Most is not all and we can debate where the "affluent" line is, but cars are useful things especially in a country mostly built around cars.
Again, most is not all, and affluent households does not equal all affluent people. That lots of people own cars does not mean developers should be required to provide one parking space per tenant, especially in places with decent mass transit.
