I tend to agree with Stan. There is a lot of research on the size of the market, specific market segments, features required vs. desired for each segment, etc.
If you look at it by price point, you have FX bodies at $2000, $3000, and $5000. You have DX bodies at $600, $1100, and $1900 (D300s or probably D400 later). And you have multiple price points in the Nikon 1 lineup.
There is a lot of work done to be able to deliver products at a specific price point while not reducing gross margin. It's not just features you give up with lower priced models - there is also a cost reduction through scale economies of re-using previously developed technologies. And at the end of the day, they can only spend so much money for a $2000 price point.
The other issue with FX bodies - especially high megapixel bodies - is the lenses are expensive as well. There are plenty of lenses for the high end, but for the pro-sumer or consumer FX user, Nikon had to come up with kit lenses matching the focal lengths most frequently used. The 24-85 VR, 28-300, and the fixed f/4 lenses are all geared to general use on the lower priced FX bodies.