The gap between acquaintances and friends in Japan is emptier than the one that I know in the U.S. That is, you're either one or the other; this makes it difficult for Japanese to make friends, but once they make them they stick to each other like flies on sugar.
I think this has a large part to do with the in-group/out-group thinking, and the feeling of obligation/responsibility for each other.
I'll write more about this soon.
I feel like Lost in Translation expressed that. You know Ebert and Roeper were saying they had tons of people yell at them for recommending that movie so highly. They didnt' like it, saw it after it was on the big screen anymore. They think it's doesn't translate well to the small screen, you need the big screen to sense the isolation.