OK I’ve not been through many airports at all, but in the other airports it’s obviously been considered that I’ve been through the x-ray & passport-check thing when I’ve got on the ‘plane in the first place; when getting off one ‘plane at HKG and onto another, there’s no need to stand in yet another line & rifle through my bag for liquids/passport/laptops/etc.
At every airport in Asia, when transferring between international flights, including HKG, you need to go through security when getting off one plane and onto another.
The difference between SIN (and KUL. CMB, SUB, DAC and maybe a small number of others) and most other airports is that at SIN you get off the plane and are immediately mixing with departing passengers, and only go through security when boarding.* At HKG and most airports arriving and departing passengers are separated and you are channeled through security first before entering departures area. Thee is no simply getting off on one plane and onto another (in Asia anyway). anyway, other than domestic to domestic)
* except about 1 in 4 or 1 in 3 arrivals from secondary SE asia destinations which do often have “special” screening on arrival as well.