Seems kind of strange to have a "hub" at one end of the country. A wheel hub is not on the edge, it's in the center. Hence, SFO is a hub for flights to Asia and Europe. The Bay Area is quite wealthy and generates substantial traffic to Asia and Europe, which UA helps to meet. I fly to Germany a lot and occasionally to Japan. I wouldn't join AA's program given those routings. Sure seems like UA dominates the I-terminal.