In both Japan and the U.S., I have lived/am living in an apartment complex. That means that people who live in the building will occasionally pass by me. In Japan, with rare exceptions, most people would give a friendly greeting when we walked by or respond in kind when we offered a greeting first. This was in no way an indication of friendship, but a perfunctory act of civility. The fact that people always responded to "ohayo gozaimasu" (good morning) with a similar reply carried a certain feeling of balance and comfort.
In the U.S., my experience has been greatly less uniform in this regard. A handful of people are friendly and reply in kind, but some seem actually irritated or taken aback when I say, "good afternoon" to them. The sense I get is that, though we occupy the same apartment complex, they feel burdened by having to interact with me in a minimal fashion. They would rather we walked past one another with downcast eyes as if we were random strangers passing on a street. The inconsistency of response makes you feel some stress when you greet people, and lowers the chance that you'll do it at all which in turn creates a colder atmosphere in general.
I don't think it's asking too much that people who see each other around the same little patch of land on a regular basis exchange a few words in greeting, and certainly it seemed in Japan for the most part that they subscribed to this belief as well. I miss the way in which social propriety carried a sense of being neighborly.