The above replies are correct, WN does not assign seats so they can turn planes much much faster than the other majors. However, as a frequent passenger on the PHX-AUS runs last fall, I can attest the fastest turn I witnessed was 27 minutes. So much for the 20 minute turns they used to do a few years ago. They recently became more unionized. You be the judge if there's a connection.

As I see it, the two downfalls of WN are the lack of assigned seating and the FF program. They have no airline partners, and their free tickets expire in a year. Pretty hard to go anywhere but their destination with Rapid Rewards.