Why do some US airlines keep operating their overseas hubs, UA and NW in Tokyo, but others are abandoned? I'm thinking of DL not continuing service from FRA that they inherited from PanAm. Also, are there other examples of airlines with overseas hubs?
This question is related to a couple of older Delta forums, but broader in scope.
http://www.flyertalk.com/forum/Forum21/HTML/006244.html
http://www.flyertalk.com/forum/Forum21/HTML/005559.html