Really? That hasn’t been my experience — and granted I’ve never lived in Australia or spent much time out of Sydney but I was there for 10 days in February and even though I paid for 4G Plus or whatever Optus calls LTE, speeds weren’t even comparable to what I can get in the US and were truly behind what I got in Seoul (where I was right after I was in Sydney). The only research I’ve seen that indicates Australia is amongst the fastest comes from research that is based on maximum speeds, not average speeds.
I can appreciate that Australia has robust cellular networks (assuming the user doesn’t live somewhere where they are forced to use satellite), in part because home internet speeds are so poor, but I wouldn’t put it in even the top 10 of parts of the world I’ve visited for internet speeds.