Airlines have been using yield management since the sixties. Maybe the new ones think they have a better model? Easy seems to, I read once they see their software as giving them a competitive advantage which can be applied to car rental, internet cafe pricing, cruise ships, la de la de la. So the legacy airlines will also sell you a cheaper seat if you book in advance. Where I suspect the newbies differ is their corporate culture values the customer who pays £1.99 equally to the customer who pays £199.99. The legacy carriers don't see it this way.