Australian airport and downtown duty free interests were all bought up by Hong Kong interests, and since then prices, particularly alcohol, have become too high. Best to buy on arrival in UK, etc. Although good malt whisky can be bought for similar prices in supermarkets there.
This really does not surprise me at all, I was thinking a similar thing when I went through HK recently and was told AU customers are not allowed to buy liquor as it will be taken by security before boarding (I've only been through twice). Made me think there was some kind of weirdness forcing people to buy from Australian DF stores. HK could easily do what Changi/J'Berg does and use the bags / return to customers after security to allow the process.
Can you confirm this has happened one hundred percent?