yes, UA doesn't fly HK-Shanghai...Tokyo and Singapore are currently the only two Asian destinations to/from HK...
this will change on Dec 15th though, when the flight SFO-HKG-SIN is changed to SFO-HKG-BKK...i'm really not sure why they made this change...why isn't the route HKG-BKK better served by another star alliance member TG ?? i think there'll then be no direct flight HKG-SIN on any star alliance airline...or maybe it's another sign that Singapore Airlines will be joining the alliance ??