Everyone should read this article. [http://au.gamespot.com/features/why-australian-game-prices-will-not-drop-6401518/?skipmc=1]
Short story: because they can.
Long story: For a long time before digital downloads, the gaming industry threw around a whole heap of shifting explanations as to why we'd pay $100-120 for a new release of a game that was fifty bucks in the US. Originally, it was the fact that our dollar was worth much less than the US dollar.
When our dollar achieved parity and actually became worth more than the US dollar due to the mining boom, prices didn't go down. Then, it was the "prohibitive cost" of operating retail stores in Australia. Anyone here with an economics or business degree should understand why that's retarded - if the AU dollar value is low, they charge more because the USD price equals a higher AU price. If the AU dollar value is high, they charge more because stuff like rent, shipping, wages etc. have to be paid in now-high AU dollars, increasing operating costs in USD. So regardless of whether the dollar is high or low, we pay a $100 AU for a game that costs $50 USD. It's lose-lose.
When people called bullshit on that, they said it was because Australian minimum wage laws (we have a vastly higher minimum wage than in the US) gave our consumer base more liquid cash to spend on games. Ignoring the fact that minimum wage laws only apply to people working minimum wage jobs, and the disparity vanishes once you get over $40,000 dollars a year, the reason why our minimum wage is higher is because there's no tip culture in Australia. In the US, it's practically mandatory to tip your waitress, and a lot of their income comes from tips. In Australia, nobody tips. We've just never done it, and we've never had to, becase we don't have a retardedly low minimum wage.
And when Steam and digital distribution came along and made things like rent, shipping costs, and employee wages totally irrelevant, the retail stores...said nothing, and kept charging us out the butthole. Because they'd always been doing it, so they knew they could get away with it, because we as consumers were used to paying a hundred bucks for a game for no reason. And Steam kept the prices up (Steam is cheaper than retail, but there's still a disparity between AU and US Steam prices) due to pressure from the publishers who don't want to upset the retail chains by letting Steam charge us for how much the game is actually fucking worth.
We're getting screwed because we've always been screwed, and we've never known what it's like to not be screwed. If you want a picture of the future of the Australian video game retail industry, picture a boot stamping on a gamer's face - forever.