If you take public trans all the time, then you're doing a lot of walking. Trans takes you close enough but the 'last mile' is always on foot. That's a decent amount of exercise, at least compared to someone who is always driving. This is how I grew up and when I was older, the move to the suburbs was pretty jarring. Everyone got fatter as we stopped getting all that city walking. Worse, the suburbs didn't have a lot of healthy food options. So you drove more and ate crappier.

A pack of cigarettes in NYC is around $13. In a poor rural or suburban community, its half that. A lot of the urban poor simply can't afford smoking anymore. This must certainly affect things, at least as much as anti-smoking PSAs.

NYC also has 1.1m Jews, who tend to have a slightly higher than average life expectancy, especially the religiously observant who follow strict dietary limits. That might skew things a little as well.