I don't think this is correct - when I flew JFK->CUN in January, not only was the DirectTV on during the flight, but I was surprised to see that the service remained available until less than 30 minutes before we landed. We did travel fairly close to the coast of Florida for most of the flight, but on the last bit over the carribean, we still had the TV for most of the way.

Now when I flew Frontier back to DEN from CUN, we didn't get signal until we were much closer to the states. Furthermore, Frontier always announces that they "loose the satellite signal" outside of the United States, so I don't think its a licensing issue.