Interesting...
I had seen on TV, a similar thing. When the Disneyland Park was inaugurated in Tokyo, the American trainers had to teach the new Japanese staff how to smile.
I guess there is some truth, cultural or physiological, that supports the lack of smile in oriental people. I have also read somewhere that Japanese people consider a person foolish/stupid if he/she smiles alot. That might explain somewhat, the inhibition or avoiding smile. You can always see how serious they look, in almost every occasion you come across them.
The Mixed oriental (Indo-Chinese), i.e. from Phillipine or Thailand, etc. are a bit different. They do tend to smile more often. I have a coworker from Thailand, that dude is always happy, and thinks the people from Sub-continent, India Pakistan are too serious, pessimistic all the time...