I believe the Hong Kong gate check is required for both US and Australia-bound flights because both countries don't allow liquids greater than 100 ml to be taken on board whether bought in the sterile area or not. Most other countries don't worry about this, given that they've been "screened', hence no gate-check for liquids to Canada, Europe or Asia. I believe Australia has yet to come to terms with metal cutlery on planes, hence why Hong kong still has plastic knives in use in the lounges.