I think that WN has a smaller and more homogeneous customer base, customers who have chosen to fly WN, and customers with lower expectations.

DL has about twice as many customers, and a wider variety including a large number who pay more to fly DL and thus have higher expectations. Also, close to half of DL's customers didn't choose to fly DL, but were acquired, mostly from NWA, and many of these PMNW folk, myself included, aren't happy with the major downgrades in website and general computer capabilities, customer service, and FF program (though I for one do like Biscoffs).