The farther up the line you go, the finer the details and quality of the furnishings. You still get the same frame, chassis, engine, roof, walls, insulation, etc. in the Dutch Star as in the higher end models.
Take a look at the floors, ceilings and furnishings in the higher end models compared to the lower end. The Mountain Aires and up will have the fancy mirrored/lighted ceilings and fancier flooring while the lower models won't.
One thing that may add to the price of the higher end models is that they come with an Aqua Hot system that is pretty expensive, while I believe it is an option of Dutch Stars. My Dutch Star doesn't have as much of the Bling (for lack of a better word), but it is still plenty luxurious enough for us and the quality is second to none IMO.
I'd really like to have a MADP, but can't see paying 50% more for basically the same thing I already have except for a few more eye pleasing amenities.