I do wonder why at HKIA they have these rules in the first place. I have had several 12 hour plus layovers in HKG and chosen to go into the city, refreshing up a bit at a restroom before talking the HEX. It would be nice to be ab;e to take a shower at the lounge after a 15+ hour flight before leaving to enjoy Hong Kong proper.
I understand that the lounges are not meant to be an arrivals lounge, but in this case, I'm connecting and require a ticket to prove that. And if I never left the airport after arriving from my first flight, I'd still have access to the showers etc. as soon as I hit the lounge first thing after clearing transit security.
If I wanted to go into town, I'd still have to clear immigration etc. both leaving and reentering the airport, but that would be my choice. In the US, one needs to clear immigration and customs after an international arrival, but after that no one is going to stop you from clearing security, going to a lounge to take a shower, then leaving the airport during a long layover, to return later for your flight, be it a domestic US or another int'l flight.