My sister-in-law has an optus wireless internet thing. She can barely keep a connection up, never mind download lots. This is in suburban Melbourne. Skype lasts a couple of minutes before dropping out.
My guess is a lack of towers and perhaps the Australian penchant for corrugated steel roofs.
I don't think data for information is much of an issue. The big hog is video, which is mostly unnecerssary and not that great on a mobile screen.
It doesn't matter too much - cables are better.