That's just because the Marxist way of thinking has pervade…

That's just because the Marxist way of thinking has pervaded everything. Class is like classification--it's just a way of dividing people that sheds light on our sociology. Does separating people in terms of wealth do that? I would argue that no, it does not and that what the mainstream media calls the "lower class" has a lot more in common with what they would call the "lower class" than the "middle class" has with either of them. I see leftism as an alliance of the "lower class" and "upper class" against the "middle class" and I call these two groups upper and lower class, in accordance with libertarian class theory.