Busses and jumbo jets have a great deal more seats than small cars and airplanes. It may, however, be the opposite. It is currently believed that the number of seats may be a result of polyploidy in which an error occurred during meiosis that resulted in a doubling of the number of seats within the structure. The size of the structure would logically have to be altered in order to make room for the new seats. An interesting development in the evolution of the plane is the polytirical evolution that occurred.
Planes have only three wheels while autos have four.
This is logical since it is much more common in nature for features to be subtracted than added. This may have also been a beautiful case of natural selection in action, however. The automobile has four wheels because this is the most stable construction for it as it needs equal stability on all sides to counter the centrifugal force involved with turns. The plane, on the other hand, only uses it's wheels for landing so turns on the ground are of little importance to it. For landing, three wheels is actually more stable.