jfb,
While you are right about Model Power lights being cheaper, I think it is mainly because they are incandescent where as all of the newer more expensive lights are either LED or Fiber Optic and are more to scale than the Model Power lights.
Don't get me wrong, I use Model Power lights because they are cheaper and I think they are good for what they are, not to mention the incandescent lights do seem to be more realistic, light wise, than the LED variety.
I also agree that many of the other manufacturers lights ARE over priced, no matter what they are.