AmEx has worked hard to keep their home turf around New York City friendly to their cards.
They did this campaign in Sydney a while back.
Used to be every year, Amex in Canada would run a "Shop Local" promo where you'd get $5 back on a transaction over $10 at smaller places x5 in a month, and let you look up who's a part of the program on a map.
Then you'd visit a lot of them and they'd claim to not accept Amex!