Question for Australians.

.uʍop ǝpısdn ǝdʎʇ sʎnb noʎ ʇɥbnoɥʇ ı

I'm a Kiwi instead, but I can answer your questions. Australians do use US$ prices in the Steam regional store. Some games will be listed at the same price as the US release, while others will be listed at a higher price. The games are individually priced, and so some mistakes can be made when they intend to do a Australian special price, same as price errors in any region.

We always get ripped off in the price department.

Example:

• DOOM - $60 USD on the US store | $80 USD on the AU store.
• Battleborn - $60 USD on the US store | $70 USD on the AU store.
• Call of Duty: World at War - $20 on the US store | $40 USD on the AU store!

It's a joke as we already pay in USD & not AUD. This is the reason why I now avoid buying from Steam if possible. I've even started buying from the grey market as a direct result of our jacked prices.

Explanation part 1
Explanation part 2
I've read better explanations in the past, but can't find them right now