I don't know about the intent of the author here, but there are huge salary gaps between rural and urban locations; even after controlling for cost of living a gap can remain.
I agree. My salary at my IT job pays about 20k less than I would get if I lived 3 hours east of where I'm at. While it's considerably more expensive to live there, I am still losing about 10k / year.
True, but there are also significant cost of living differences between urban and rural areas. More generally, there are valid reasons why some people enjoy living outside of large urban areas, and I don't think dismissing them as undesirable bolsters the author's argument.