they advise 2 hours before just to be on the safe side. if everyone came 1 hour or 40 minutes before... there will just be loads of people complaining that they were there but are not allowed onto the plane because they were checked-in late. also, if you tell people a certain time, they will likely get there late anyway - that always happens when anyone tries to organise a dinner or gathering.
unless i'm really short on time, i get to the airport about 2 hours before, and usually, im only waiting about 10 mins to board. it takes a while to check-in, get through security, walk/take the train to the gate (HK airport is pretty big), buy some water, maybe some snacks for a long haul, and probably enough time for a wee so i dont have to wait in the queues whilst on the plane.