Your links are unfortunately misleading. Your US numbers are from 2011, while the Australian numbers are from 2007-2008. Additionally, the Australian numbers are PPP or "Purchasing Power Parity". PPP allows comparing of currencies insofar as what can be bought, rather than the pure exchange rate. While PPP may be a useful way to compare different countries, it is inappropriate in this discussion, as the point being made is that Australians pay more than they should for products. I don't have recent numbers for Australian median incomes, but Wikipedia's page on GDP per capita:
Places Australia at a GDP per capita at between $67-70,000 while the US is at $47-$50,000 per capita. Not the double in income that the original poster said, but still about $20,000 ahead.