Australia only has something like 26 million people in the whole country of course there's going to be less nutters and less of a chance of bumping into one. Our 2 biggest cities have more people than the whole of Australia, that means we have potentially the same amount of maniacs in those two cities as all of Austrailia. If you took half the maniacs in Australia and put them in an area the size of NYC, of course it's going to be scary. You have the spread over an entire continent. You also have a much more "homogeneous"population as do the Japanese cities.