Like a good social scientist, I developed a theory to explain this behaviour. I call it the 'hug or hit' rule of social engagement. This rule states that Sydneysiders (and possibly all Australians) feel that we have the right to interact with strangers if we feel like it, and the obligation to respond if people interact with us. We feel that we should be able to treat each other as intimate friends, even if we have never met before in our lives.
However, we also feel that we have the right to reprimand other people if they don't behave in accordance with our social rules. In other words, our claim to intimacy makes us social and antisocial at the same time.
The English have exactly the opposite rule. Indeed, not only should you never talk to strangers; you aren't even allowed to give away the most basic information to people you meet in private. Standing next to a stranger at a party?
You can talk about the weather as a way to break the ice, but don't dare to offer your name, or ask the other person what they do for a living.
In her hilarious book 'Watching the English', Kate Fox explains that if you want to get to know someone, you must trick them into giving you information by asking indirect questions. 'Nosey parker' is the worst insult that someone can throw at you.