You are correct medhead, it doesn't sound correct, but it is.
One of the lovely quirks of Australian (read Federal) Liquor laws. As any traveller departing Australia, you are eligible for duty free shopping. But under the Liqour laws, excise is excluded for Australians. SO, consequently, all duty free prices are displayed including the excise. As a foriegner, you are entitled to claim that excise back under the TRS. But, of course, it is not well advertised.
Australian citizens, are unable to claim the excise back. So, under the duty free laws you still pay the excise. (there are some circumstances were the WET is excluded, but I'm totally up to date on that). The prices in any australian duty free outlet, only exclude the GST. (which is a tax on a tax, I know. But welcome to Canberra beauracracy)