UA at IAH leaves me befuddled. They essentially ceded Texas to AA/DFW and are retreating in Mexico markets while AA expands. They’ve cut a ton of Southern markets like MGM, TLH, CHA, CAE, CRW, etc... all while the city and region continue to grow. Just spent a week on business in central Houston and there are cranes everywhere.
In addition to DEN and ORD being better connecting points for east-west connections, there are other factors weakening demand for UA service out of IAH, including the following:
(a) Further domestic expansion by WN at HOU following the UA-CO merger,
(b) WN adding nonstop international flights out of HOU starting in 2015,
(c) Post-Wright Amendment expansion at DAL by WN,
(d) NK entering the IAH market in 2012,
(e) F9 adding a few more nonstop routes out of IAH,
(f) The expansion of AA's DFW hub, including the addition of a few additional domestic nonstop routes.
WN also has some additional stations other than DEN or MDW that are better connecting points for east-west connections than HOU such as ATL, AUS, BWI, DAL, MCI, LAS, BNA, PHX, and STL.
AA also has hubs at PHX, DFW, and CLT that are better connecting points for east-west connections than UA's IAH hub.
While UA has dropped nonstop service out of IAH to some small regional destinations in the Southeast and Midwest, UA still has nonstop service out of IAH to some small regional destinations in the South, the Mountain West, and the western half of the Midwest.
There are also a few smaller markets in Texas and the Florida Panhandle such as AMA, LBB, MAF, ECP, and PNS that are still served nonstop from Houston on both UA and WN.