I agree with the results, HKG & SIN are great airports (I've not been through SEL), ZRH & AMS are the best in Europe. Actually it is airline not airport surveys where I sometimes disagree with the results.
LHR is better now that T5 has opened. It wan't a bad airport but it was operating way over capacity, terminals congested with passengers and certainly in my experience you had long waits to get onto a stand at T4. At times you thought yourself lucky if you got a remote stand with coaches waiting.
If you asked people to list their favourite and least favorite airports LHR would probably appear on both lists (a bit like Margaret Thatcher when PM). Favourite because of the range of flights, least favourite because of the congestion. The airlines want to go there because the yields are higher which suggests that premium travellers at least like the airport, or ais it that the alternatives (possibly excluding LCY) worse?