The contrast with my experience on the London underground was striking. In fact, I was rather confused, because I know that Australia isn't always as friendly a place as my observations suggested. Just as in any other city, most people ignore each other as much as possible.
Moreover, people seem as equally ready to throw insults and punches at each other, as they do to compare lottery results or buy a stranger a drink. A night out on the town in Sydney might result in a new best friend for life, or a black eye for a week.