I guess it depends how you define "large swath". Is it a certain amount of landmass or population, a percent of total landmass or population, or some other metric? I think this line is needlessly pedantic. It's reasonable to interpret rubidium's comment as just meaning "the expensive housing in the NY and SF areas are too expensive to be feasible for top 20% earners, as the OP said, but by and large, a middle class existence is possible for most land in America." Population centers with expensive housing may be inaccessible for the regular middle class (when top 20% income earner means only 60k/year or so based on 2010 data[0]). This isn't really the right data to use, because the pay for people in SF is different than say, somewhere in Missouri. With that being said, it seems clear that the American dream of a middle-class existence with only one working adult, isn't realistic everywhere for everyone.
I might be meandering here, but I think this reasoning is actually flawed or biased, because it was never true to begin with. A factory worker could never afford to live in the upscale street, right? The only difference now is that instead of a factory worker not being able to live on the upscale street, there are whole neighborhoods, downtown areas, and maybe even suburbs that are unaffordable to a typical middle-class family.
I haven't looked for data to support these ideas, and am very open to points for and against.
