Question About The NYC Tri State Region: Is It Transient? (New York: transplants, home)

[Thruway]

I was orginally born and lived in the tri state area and carried my roots with me while I was transplanted into metro DC.

I always thought the DC area was best exemplified by how whenever they played a popular team from the Northeast at home it was loaded with NY, PHI, or BOS fans.
One of the reasons was, not only is the DC area a bad sports market, but it's extremely transient.
It is filled with people who were not born there and have little if any affiliation with the area at large.

I figuered DC and other exploding new southern cities were this way.

New York always struck me as being different, not only as a mega market, but as a more homogenous one with natives being born proud New Yorkers and carrying their roots in whatever manner, be it sports teams, with them.

I did not think New York was another DC, an apathetic, poser sports town filled with transplants.

However, whenever the Yankees play the Red Sox there always seems to be a ton of Red Sox fans at Yankee Stadium.
I've read not that but there are many Red Sox bars in New York.
I also remembered some Redskin fan telling me there are a lot of Redskin fans in New York, and Redskin bars too.

I wondered to myself how can this be, I thought New York was a diehard, passionate sports town and city that took pride in their own much like Boston and Philadelphia, other North East towns.
I did not think it was an apathetic DC, Florida, or CA cultureless, imitation market.

I stumpled across this site below, which if lists nationwide each county and where people are migrating in from and out of.
http://enterprise.star-telegram.com/ARCIms/Maps/clt/2007/irsmig.asp?map.x=392&map.y=31&pick=&action=bg (broken link)

Surprisngly it seems New York isn't that transient, but Suffolk, Norfolk, Middlesex counties, all MA, were some of the top out of tri-state places that people came from.
Also near the top, surprisngly, were
Cook, IL (Chicago) 6,234
San Francisco, CA 5,833
Middlesex, MA (Boston) 5,172
Suffolk, MA (Boston) 4,841
District of Columbia, DC 4,041
Miami-Dade, FL 3,615
Philadelphia, PA 3,576
Montgomery, MD (DC) 2,390

My question; is the NYC a transient area that is rather soft like DC, or is it a hardcore, strong homogenous region without much transplants or those who come into NYC quickly get engolfed and become NYers as opposed to sticking to their old towns?
Is New York like DC or is like Boston in that it is homogenous with a great deal of local civic pride that transcends newcomers inland and abroad, but due to shear size and it being the entertainment, financial spot in America, not as homegenous as Boston but still nothing like DC and moreso, having such high "New Yorker" pride a place where newcomers usually don't stay with their roots of other towns but become "New Yorkers"?

Second question: Why are there evidently so many SF, CHI, BOS, DC, and Miami migrants?
Is NY a place with a lot displaced people from those markets, or just Boston with the others likely being displaced NYers coming home?

Thanks.