Originally Posted by Sebring

That particular flight is often affected by the atmospheric wind patterns, and if there is unusual, and persistent deviation from seasonal averages, it can result in a long run of lateness.

Eastbound, the flight can get a tremendous tail wind. Flights have been known to achieve cruise speeds in excess of 700 mph over the ocean.

Here's a current model of the jet stream. Going North over the pole, or the old route over the Pacific to HKG, you'd hit significant winds.

http://squall.sfsu.edu/gif/jetstream_pac_h120_00.gif

Also, airlines don't usually adjust schedules once they are issued. It would lead to too much chaos for both passengers and crew scheduling.