Isn't this just a regular issue at HKG?

Many, many months ago I took a can of grape Fanta from the UA RCC for the short hop down to SIN. At the bottom of the jetbridge, immediately before you got on the plane, they were doing checks of bags, and removing all liquids over 3 ounces.

This was not a flight to the US, although it was on a US carrier.

I would never try to buy liquids after security in HKG, but I've never had this problem in NRT or SIN. Never departed PEK or PVG for the US or on a US carrier, so I don't know if they operate in a similar manner to HKG.