Median Household income in the US is about 50k USD. That's across the whole US, podunk cow towns to NYC. The Australian "capital territories" are averaging 60k USD per household. Across all of Australia it's 43k USD.
Not 43k USD, 67k AUD which is around 64k USD. The 43k USD figure you've quoted is adjusted for purchasing power parity (PPP) - it already takes into account the higher prices in Australia. So just looking at income, you're right that Australian incomes aren't double the US, but they are actually quite a lot higher.
In any case you've used different metrics for each country. This table shows equivalent metrics for each country. Australians clearly earn more, but are just a little behind on PPP. Of course, that table shows 2010 data, and Australia's economy is doing quite a lot better than the US - I would be surprised if Australia hadn't already overtaken the US on PPP.