Culture does a lot to mold people. I've noticed just as you said that Asians who were raised either outside of the Western cultures, or who were raised here but who were not yet totally Americanized tend to be very respectful/polite/hardworking/proper in public, and tend to be real freaks when the doors are closed. The public ethos that they display has pretty obvious origins, given that Asian culture stresses hard work, demands excellence, and comes with a strong sense of propriety. Why are they so freaky sexually? Well, perhaps for a number of reasons. Keep in mind that "Asia," and by that I assume we're talking about China and SE Asia, was largely insulated from religions like Christianity and Islam for most of its history, which meant that they never got bathed in the sexual values of those religions, which tend to be very conservative sexual values. Western culture is far more prudish than most of us realize.