Just to clarify, thats not really steam's fault, its the publishers fault (as you point out).
I think the high prices in AU started because of the extra shipping cost they have to pay to get it over to the island. However, there's NO excuse for that with digital versions. I know the publishers are afraid of cannibalizing retail sales, but in AU they'd have a good reason to, because they'd make a lot more profit by avoiding those high shipping costs. Besides, its not as if retail sales in AU are going to be a huge factor compared to europe, etc. They could test that marketing strategy over there in fact, and see how much retail they'd lose if they offered the digital at a reasonable price.
While I don't attribute the blame to Steam for it being done, I do believe they could be a bit more proactive in trying to help fix the problem. The're not making the decision, but they have to assume part responsibility IMO. It's all too easy these days to just turn a blind eye.
I don't believe it was even about shipping, it's really just greed. They should save a fortune shipping it over in bulk, especially considering I can buy it myself and have it shipped over for far less. Why the cost almost doubles beats me, but they should be ashamed for it.