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.)