It's kind of true, though I found americans to be pretty friendly on my various visits to the states, even in NYC, which has a reputation for having tough people live there. Though I did get major, major attitude from a lot of department store clerks. Geez, I have a bad job too but please don't take it out on me! Whatever happened to customer service?
But yeah, I don't know. It depends where you are. Sometimes people start random conversations with other people on the city bus. And if you're out in the country and you're driving past somebody in another car, they ALWAYS wave. Even if you're a city folk and they don't know you. Unless it's someone like you who isn't from that town; then they don't wave, lol.