In most cities, they probably do or have fairly restricted ability to get around. NYC or even SF aren't typical of the US as a whole.

Zipcar, Car2Go, and Uber have done a lot to alleviate that. Car ownership is definitely not needed in Seattle, Portland, NYC, SF, and probably many other cities. In the rest of the US, most exceptions are because the US doesn't do cities well, largely due to the perception in the mid-to-late 20th century that white people had abandoned the cities and left them to black people, and America doesn't care about black people.

Something like 50% of all trips are by car in SF! I'm guessing NYC is better.