My point was slightly different. If you want to go skiing for the weekend, you either have to carpool or rent a car of course. But in NYC (or at least Manhattan/parts of Brooklyn), there's just a general assumption among your local friends, organizations putting together activities, etc. that neither you nor a lot of other people have cars.

By contrast, with a group of paddling friends, some of which live in Cambridge, everyone has a car and while we'll carpool where appropriate the (correct) assumption is everyone has a car for gatherings and activities.