It varies from port to port. As Pook says, at HKIA there are people whose job it is to stop people taking oversize bags onboard (this is not airline specific). Overweight but OK size tends not to be spotted unless the bag is obviously very heavy.

CX at HKIA and some other ports have tags which they will give to Premium passengers on request to enable them to take a reasonable extra amount of cabin baggage through the checkpoints. Premium certainly includes First and top-tier Marco Polo members. Not sure about business class without status.

But there is a reason for this limit - the safe load limits on the overhead bins. Frankly I would prefer not to have them collapsing on top of me in the event of a heavy landing. Cathay's rules are not significantly different from other non-US airlines in this respect.

And if you have cabin size baggage that weighs more than 10lbs empty one has to ask why? Have you considered getting better bags?