Urban environments can often be less noisy than suburbs next to highways/freeways; due to extensive use of subway infrastructure - which moves the associated noise underground. Also, a suburban commuter spends a lot of time in a car commuting, being subjected to the very noise the parent poster is referring to.
I think that's the more minor part of the noise that the original comment was referring to. It's much easier to insulate one's detached house from suburban noise than it is to insulate one's apartment from noisy neighbors on the other side of a shared wall. It's also my experience that those noisy neighbors are a much bigger nuisance than the traffic noise in the first place.
On a tangential note, I'd be curious to know whether you have any links to back up the claim that urban environments are often less noisy. I don't disbelieve the claim outright, but it sure doesn't match my personal experience.
