Jeff, clearly, inflation, alone had an impact on what is now "low income" v. "middle income". But this article I think points to the fact that those $30K/year jobs that used to be available for low-skilled jobs, have disappeared. Like the receptionist who is no longer needed for answering phones, or the low-skill manufacturing jobs that disappeared. Even if $30K wasn't worth so much less today, there would be (are) less low-skill jobs available.
Actually, I don't blame the politicians as much as the teaching philosophy that decided "self esteem" was more important than actually learning well enough to have a grasp of the subject matter. Even now, teachers' unions object to "grading" teachers by how well their students perform.More on the topic of this thread, I believe that our loss of competitiveness in the global economy is directly linked to the growth in anti-intellectual and anti-scientific beliefs. This was a cornerstone of the Reagan presidency, and has become an increasing part of political campaigns since then.