Working class: One who makes money by collecting a wage.
Upper class: One who makes money through investments or similar business dealings.
Middle class: One who partially makes money by collecting a wage and partially through investing.
Wealth figures are more difficult to come by, but the internet suggests the median household has a net worth of around $200,000. However, I would venture to guess that a large portion of that is tied up in a primary household which does not normally generate any income. It is not clear how much a typical person does make in investment income.
If you are right that 60% of the population do not have investment income, that seems reasonable enough. I think it is fair to say that most people are working class. I am sure that we can agree that, under modern usage, the middle class is meant to represent something that is not easily attainable, but more attainable than upper class.