Accents?

Out of curiosity I took this test today:

What American accent do you have?
Created by Xavier on Memegen.net

New York City. You are most definitely from New York City. Not New Jersey, not Connecticut. If you are from Jersey then you can probably get into New York City in 10 minutes or less.

Take this quiz now - it's easy!

We're going to start with "cot" and "caught." When you say those words do they sound the same or different?

Same, no wait I mean different, maybe, a little bit different... Different Same

Considering that I actually learned Queens English in school, and have since conversed mostly with people from Britain, I guess this does make sense somehow. At least, comparing my own accent to that of different American guys I spoke with, New York Accent does seem to be the one accent that comes nearest to mine, anyway.  ;-)
However, it made me wonder... why is it, that New York Accent sounds so much more British than all the other American accents? Historical reasons? Migration? So many foreigners, that the accent kinda "evens out"???