I agree. I grew up in Illinois and now live on Long Island. My husband grew up in Queens, NY and notices the difference. My adult children notice the increase in friendliness as they travel westward, too.
I do think that, since 9/11, many of the folks on Long Island are much friendlier than they used to be.
Nothing has changed since 9/11, IMHO. The 9/11 effect lasted all of 9 months in the city, and a year in the suburbs. Everyone then returned to their self-absorbed lives.
Also, there is more competition for space here. My mother moved from a Chicago suburb to live with us, and can't get over the way in which everything is shoe-horned into little spaces. Doctors' offices are unbelievably tiny with crowded hallways. Drivers are very competitive for parking spaces at doctors' offices and shopping centers.
When I first moved to Long Island, I thought I would suffer from claustrophobia for the rest of my life. I lived at a greater distance from NYC than I had from Chicago, yet streets were more crowded, building lots were smaller, houses practically bumped up against each other. Most backyards in the sections of towns I have lived in are too small for playing sports. (There are some beautiful town parks, but kids who aren't playing a scheduled game aren't allowed to "mess up" the playing fields.)
Ordinary commutes last longer here than they did in Illinois, so the average dinner hour for commuters' families is later.
Not that any of this is an excuse for bad manners.