Difference of relationship b/w the U.S. and Japan

Considering New York and Tokyo, both cities are big, fast, and busy, but no sooner did I start to live in N.Y. than I realized people’s relationships are very different. Compared to Americans, whose relations are wide and shallow, Japanese relationships are narrow and deep.
For example, American people seem very friendly, chat with people who they just met on an elevator or on the subway while waiting. I hardly ever see such a scene in Japan.
Another example occurred when I first went to a party like a house warming party or the 4th July party in N.Y. People there looked like they were familiar with each other. It wasn’t until I had asked my friend that I found they were not friends, even though they knew each other, they had met just once before. Unlike in Japan, in the U.S. people have a lot of opportunities to meet different kinds of people, because usually Japanese don’t invite the people who don’t know each other.
However, the Japanese way of relationship is sometime good. Especially in companies, relations of most American people are light and superficial. They are just coworkers, and usually they don’t hang out. On the other hand, Japanese relationships are tight like a family. They spend their time even after work, and sometime visit each other. In my opinion, it’s good for running of business smoothly.
The gap of those relationships comes from the difference of their way of thinking. Americans believe the individual is important. In contrast, Japanese tend to care about their circumstances. Both of them have merits and demerits. I want to take each good point, and I think not too much is good for everything.