alvega, merry christmas to you and those who care. I'm an HKG ATC and I do agree with your observation, many of the local youngsters don't know what manner / politeness is. Ok, if it's a radar environment, it may be barely justified to skip those greetings on occasions, but in a tower environment, would someone else get delayed for greetings between ATC / pilot? Get an $x extra fuel burn (0.5 sec delay)? Well then file a formal complaint against ATC or even sue us!
But on the other side, many locally based pilots are not that polite either! (After all, who started this in the first place, ATC / pilots? I don't know.) In the past, I would initiate greetings to the pilots, but I don't do this too often now (at least to the locally based airlines), as it sound stupid especially when you have a couple of pilots in a row who don't really care. Having said that, my bottom line is whenever a pilot says good morning, I would do the same in return (unless I'm busy with something else, e.g. urgent coordination with another controller, maybe).