Jamester, as long as I can remember, flights transiting HKG have been much cheaper in all classes than those terminating/originating there. The reason is market: HKG is by far a more affluent business market than BKK, which is a leisure market (just as the Thais have positioned it). Today, an all UA RT LAX-HKG-BKK is about US$1500 less expensive in C than a LAX-HKG RT. Do some pax go to BKK and backtrack on an inexpensive flight? Of course, but very few.