Thanks for your (and the other guys posting as ACs) detailed answers.
So it's mostly a ratchet effect on the foreign exchange, with massive impact because of AUD/USD volatility.
It sucks that online platforms such as Steam are playing that game and not allow you to buy in USD at US prices... Well it also sucks for me to some extent (although online prices in Japan are not so bad - almost in sync with the US, the selection is limited, with AAA titles such as Arkham City missing for obscure reasons, etc). There used to be a time where I actually relied on Steam more, when they had not implemented regional segmentation yet. Now I am back to brick and mortar import shops or HK based outlets.