I think you need to understand the background here.
The Australian dollar being week in the period around the year 2000 meant that prices went to the ~$100 Australian for games, which at the time was a fair reflection of the exchange rate. Now the Australian dollar is at near parity with the US dollar, publishers have been very reluctant to pass on the savings, and games still retail for the same as they did when the dollar was weak.
Note this isn't just a problem for games, us Aussies get ripped off on DVDs, music CDs, books, everything. When the exchange rate goes down the prices go up, when it goes up they don't come back down.
Naturally the publishers want to maintain this situation, and so many of them are now implementing regional pricing on digital delivery services such as steam. The steam price is set to compete with the local price.
Obviously people willing to pay the shipping and handling to buy from overseas stores can get it cheaper. In the digital world, people willing to use a proxy and buy from the US can get that price too. So there are ways around the regional pricing system.The publishers know their hold is weak, but they're going to cling to the extra profits as long as they can.
Now I don't think steam is completely blameless in this, the feature of regional based pricing doesn't write itself. If they wanted to push hard enough on it they could probably eliminate it (although I suspect they weren't in a strong enough position to do so when they first signed these guys up, if they'd said no they probably wouldn't have 2K on steam at all).
So I'm not saying steam is perfect, but to blame them for the pricing instead of the publisher is dead wrong. Especially given both Valve's public statements and their own practices (all Valve's games share the same price on the AU and US steam stores) suggest they think regional pricing is archaic.