I am not sure I believe that Australians have a higher purchasing power than Americans. Certainly for an example I'm more familiar with, the game costs NZ$109.99 in New Zealand, which is US$90 at the moment. I can assure you that the purchasing power of an average NZer is less than that of an average American, so goodness knows why it has to be so much more expensive. This is fairly standard on a lot of things - books, DVDs etc - and I can only presume it's simply because they know they can get away with it because people have gotten used to games costing about $100 without worrying about what that means in the publisher's native currency.