Interesting update to us having to pay the departure tax when we traveled with Taca last month - American Express Travel (who apparently book through Travelocity) ended up refunding us half of what we paid upon departure. We disputed the charges when we returned, and even though they said they had no record of me calling beforehand (even though when you call, they mention that your phone conversation will be recorded for quality assurance purposes), they gave us a refund. It was only half of what we paid, but at least it was something, I guess.
Continental in July included the departure taxes. Did you book directly through Continental? If not, like in our situation, maybe the middle entity did not charge you, but the airline did.