The difference is that UAL flies JFK to LAX in 767's, SW does it in 737's. Customer surveys claim that pax on the New York to LAX route prefer wide body aircraft. Apparently not enough pax prefer wide body aircraft enough to pay the extra ticket costs of UAL. You do not think pax would lie on a customer survey do you? Good Heavens!
Seriously, if UAL gets its ticket prices anywhere near to the low cost carriers why would anyone fly New York to the West Coast in a 737 at .75 when they can fly in a wide body at .80?