You want to just use population as a criteria when you need to look at the economy of that community. NY, ORD, DC, LA, SFO and DEN have an economy that supports that flying. Take away oil and the per capita income falls quickly. This in and of itself causes United to force passengers through IAH to support the base/hub. This flying can easily be flown out of LAX,ORD,EWR and IAD.