I realize you're being rhetorical here, but one good way to see this is to couple the law of supply & demand with this: http://www.fastcompany.com/blog/kelsey-keith/designage/infog...

Of course that doesn't account for population density, but if you take a look at http://www.wolframalpha.com/input/?i=populations+of+LA%2C+sa... you can see that the Midwest certainly has a higher per-capita rate of McDonald's.

(I realize this is not much better than anecdotal.)

The McDonalds map has more than one interpretation. Population density is much greater, and city-to-city distance much smaller, in the eastern half of the US. In other words, the great black areas in Nevada are not due to healthful zealots, but empty space where nobody lives.