Microsoft have taken a lot of criticism of the inflated pricing of Windows 7 in Australia, compared to the US offering. With a strong Australian dollar, the US and Australian dollar are the closest they’ve been in a long time, so why such a difference ?
“every market is different and Microsoft prices vary by region and are determined based on a variety of location-specific factors including, but not limited to exchange rate, local taxes, duties, local market conditions (such as the size of the market) and logistics.”
Another important thing to consider is the US prices are before taxes, whereas Australia requires items are listed with taxes (i.e. GST).
For the full explanation, read all about it @ http://blogs.msdn.com/windows7au/