Randy1,
If HTC were to simulate the adverse effects of applying paint to an aircraft, then all of the players would be inclined to fly only bare metal skins on airplanes (if available) in AH. Now that wouldn't be fun, would it? Everyone would fly that bare metal paint scheme to get the best performance. There wouldn't be that added diversity of representing different historical fighter groups.
Part of what makes this game stand out is the fact that their players make contributions by skinning aircraft for others in the community to use.