For a hundred or so dollars, I would agree with you. For $20, it does seem a bit petty to me, as it is a very small dollar amount. In addition, $20 is not very likely to drive someone to buy a ticket on Jetblue versus SW its own (unlike a $100+ credit would sway a decision).
I guess my head shake comes from the change in relationship between the customers and airlines. Since the "low-cost" airlines came on the scene, airline prices dropped and it caused a frenzy for travelers to go with the lowest bidder. I guess I miss the days where flying was more than price.
It may be Jetblue's policy and the airfare game is to buy early to get a the best price. Once purchased, the price is locked and the airline won't try to collect more; however, I think it should go the other way, too. If I buy a ticket and the price dropped, I prefer to npt seek a refund of price difference, as I enjoy my chosen airline and the service they provide.
Just my personal thoughts.