According to the statute, "the term 'motor vehicle' means a vehicle . . . " It does not specifically say "boat" or "airplane." There may be some technical argument here over whether boats and planes are "vehicles" within the meaning of the statute, but my gut says that a common sense interpretation of the term "vehicle" will include a "boat" or an airplane.
That is an interesting perspective. I've always assumed my airplane was a "motor vehicle", but as you know being an attorney, one should never assume. Interpretations abound, and DA's and/or judges can be wild cards. I'd hate to have to "prove" in a court of law anything that wasn't clear cut.
I usually try to land in states that recognize my CCW permit. However, there are times when that is not possible. Many pilots carry firearms in the survival kits or on their person. It would be interesting to see if there is any precedent defining a boat or airplane as a motor vehicle. The FAA has no jurisdiction on firearms in planes. It is all up to the laws where you land.