Isn't it interesting that in the latest airline quality rankings the top three spots were taken by low-cost carriers? JetBlue, Southwest and AirTran ranked the best while overall the industry had its worst ratings in twenty years.
Just goes to show that providing a leading user experience does not have to mean premium price. All three are relative start-ups compared to the likes of United and American, and they have been able to structure themselves (and therefore their) costs based on lessons learned from the older airlines.
Nevertheless, with issues like number of passengers bumped per flight, amount of baggage lost, and late flights that the survey measured, it's hard to see how these three airlines would have intrinsic benefits over their older competitors.
There is also a more intangible difference between JetBlue and Southwest compared to most other carriers: the atmosphere on the ground and the plane that emanates from the staff. It is more relaxed, more can-do, more enjoyable. One can always find one-off examples at other airlines, of course, but the widespread nature of it at these two airlines (I have not flown AirTran recently so cannot comment) makes it clear there is systemic approach to managing and encouraging this atmosphere.
(And neither Southwest or JetBlue are perfect: JetBlue had its famed debaucle with passengers stranded for hours on runways in snow conditions, and Southwest is currently not looking so good with questionable maintenance practices. If you raise the user experience bar high, the punishment is extra hard if you fail to meet it consistently.)
People often think of good user experiences as uncontrollable black magic. Nothing could be further from the truth, as JetBlue, Southwest and AirTran show: even in a highly cost-sensitive industry there is room to make it a competitive differentiator. And not just for premium brands.