Andy, ahhhh, well, do you go and knock on your new neighbours door when they move in to say hello, welcome them, and introduce yourself? I do. ( some anyway, as I live in a block of flats in London - so lots of people moving in and out all the time, so I'm friendly with everyone on my floor).
Maybe by not initiating that, they think there's no point in saying hello?
Edited: 29/09/2012 at 11:09