Regarding Australia, our GST is a flat 10%, and the AUD is near parity with the USD (and has been above parity for most of the last 12 months). The price discrepancy is far greater than it should be if those were the only factors.

The Australian Competition and Consumer Commission, an independant regulatory body in Australia that oversees the Trade Practices Act (among other things), is in the process of inquiring into the so-called "Australia Tax" to find out why companies like Apple and Valve charge far more for software sold in Australia than in other countries despite the low true cost difference.