a Maine accent is a class marker
I think the same is largely true of Jersey accents, though just as in Maine I'm sure "class" only roughly corresponds with money. In fact having too much money can be somewhat déclassé. (I highly recommend Paul Fussell's
Class on this point, which I'm reading now, or at least
this article about it.)
Accents can tend to become exaggerated by people as they move away from the area where the accent is from, as it becomes more important to signal "look where I'm from" than "look how much better I am than my neighbors." Also people with "no" accent often find that they do in fact have one. Though my native speech has been eroded by 10 years of living in the West I can have an accent when angry (which is often), or for such words as "mall" and "coffee." Additionally, when agitated, I swear quite a bit more than my simple, God-fearing companions.
It drives me crazy that no one on Colorado, or perhaps any place in America outside of the East, can hear a difference between Aaron and Erin. They say both like I say "Erin." The Mary/marry/merry test is more well-known but doesn't seem to actually pop up in speech.
edit to add: I bet in NJ/NY accent can also correspond to ethnicity. The older WASP families (and the towns they live in) being less likely to have one than the barbarous Catholics. It's definitely not just an Italian thing, though. My fatha is a testament to that.