Originally Posted by
eponymous_coward
I figure LAX for the role SFO plays in UA's system (TPAC hub + O/D), and PHX for the DEN/SLC role in UA/DL's system (while acknowledging the role isn't as good because of geography): inter-Mountain West connecting hub + O/D. It's a pretty big metro area; you shouldn't want to be coughing up a few million potential customers to WN if you can reasonably avoid it.
I think the question is whether PHX still has enough critical mass once you draw off the inter-Mountain West traffic -- and once the LAX traffic US carries through PHX today starts taking non-stops. It's notable that DL doesn't have a SFO equivalent, and UA hasn't long had a DFW equivalent. (And indeed, the balance between IAH and DEN will be interesting to watch.)
There is a long, long history of airlines walking away from western hubs -- those of AirCal, Reno Air, Western (at LAX), Hughes AirWest, and PSA, to name a few. I'd hate to see it happen again; having the option of connecting on the west coast is something I appreciate.