The bottom 50-90% of the top 10% of earners is very much part of what is traditionally called "middle class". People in high-paying professional occupations such as doctors, lawyers and engineers have always been considered part of the middle class. The upper class is made up of capitalists and high-level executives, not people who work for a living.

Source: http://en.wikipedia.org/wiki/American_middle_class#Academic_...