Let's spin this around a little. By no means am I implying anything racist here, but why is it you often find black folks nodding hello to each other on the street but you don't see black to other ethnicity greetings in the same frequency? You see it on the streets of the US all the time in a majority white area. One of my pals and coworkers is black, and we were in Japan for work. Every time we saw another black person I saw them exchange the "head nod" in passing with perhaps a little "What's going on man?" Is there a special club or something? I told him if I did that for every white guy I saw, my neck would be hurting for days (got a good laugh out of him).
I don't engage in calling out fellow white dudes when I'm in Japan. I find the practice of some here in the states poor manners, so why indulge in that while overseas?
The funny thing is on one trip we were in Tokyo just before the start of the 2004 World Cup. We came across the Nigerian football team. My pal tried the head nod. The Nigerians just ignored him. I guess it's an American thing...