I wonder if this is because sitting and watching TV tends to correlate with poor diet (lots of snacking on unhealthy things while on the couch), whereas it's quite difficult to eat bad stuff while moving around all the time.
It's easy to find organic produce here but it's not that cheap (at least compared to Europe), and I'm not exactly sure if I trust it as much as I trust organic produce in Europe or Japan...
That said from my 6 month experience living in Rochester, US is much worse... (and don't talk to me about university "food" there)
NYC is technically not "America" though, so i'm not sure if I've raised a point of contention or simply bragged about how my city is teh awesum.
During that time I never had any issues with weight gain, cholesterol, or blood pressure.