Airlines often have fares in their computers that are based on what the competition is charging. But they don't always do so. If an airline thinks they can get a better yield by charging more -- even if it takes longer to sell out or even if some seats go empty -- then that's what they'll do.
JetBlue may very well feel that they offer a superior product to AirTran, and that many customers (though not all) would be willing to pay $30 more.
After all, JetBlue provides substantially more legroom -- 34 inches in most coach seats, compared to 30-31 inches on AirTran. JetBlue allows passengers to select seats ahead of time without the $5 fee that AirTran charges. JetBlue does not charge for a second checked bag (so far). And JetBlue provides an individual video screen for every seat.
Airlines don't match fares based on phone calls from customers saying, "XYZ Airlines is charging $30 less than you are, so please match their fare."