Any "low cost" carrier, Jet Blue, AirTran, Southwest etc., does not have ticketing agreements with any other airlines.
If you have a long delay or a cancellation, you have to stay with the Airline that has your money. Sometimes that can delay you by days due to availability of seats. You have the equivalent of a cash register receipt, not an airline ticket.
American, Delta, United, and most of the International Carriers, have ticketing agreements whereby if they are delayed they can move you to another carrier, to get you to your destination. They're all electronic but they all have real ticket numbers, just like the old paper tickets, that are mostly transferable amoung the airlines that have ticketing agreements.
Everybody has "change fees." If you want to make a change, you pay. The airlines can waive them due to bad weather etc. but that's about it.
Oil is about $80 a barrel now, and there are a lot less flights flying because many planes have been parked in the various Arizona/California deserts, so you generally won't find the options that we used to see. If oil keeps going up there may be even fewer flights, as more planes are removed from service.