I think that just comes down to numbers. There are only about 40 million people in Australasia compared to 740 million people in Europe and 312 million in USA.
By saying "australasia" I'd also include Japan (130mn), South Korea (50mn) and India (1.3bn) -- not China, which is notoriously insular on most levels. They sum up to a sizeable contingent that doesn't seem to be represented in HN posts (note: i'm not saying they should, this is not about political correctness).
I noticed the occasional post about Indian matters, but it looks like the other Asian communities are just not interested in HN at the moment.
