Greetings from Chatanooga, TN.
You know we wondered the same thing about "withdrawing cars" but who knows what is possible. Perhaps they need to pull the program cars from rental agencies to sell to liquidate their used inventory. Maybe this is a way for "Detroit" to get Americans to panic as this is a way to affect the average family - - screw with their vacations by not having rental car inventory. I don't really know. Actually, I thought that the rental companies owned the cars in their fleets and that they sold them when they were at 20-30k miles.
All I do know is that I was told that even if we had gotten into MCO today, it was highly unlikely that they would have a vehicle for us and that there were no other rental agencies in any better position.
As an aside, and kudos for AirTran . . . they gave us a full refund on the purchase price of our tickets. No refund, however, for the $6/segment/seat fee

That money ($24) will go "on account" and must be used within one year of when we originally bought the tickets (6/09).
Von