The article points out, more people have moved from the middle class to the upper class, than have moved from the middle class to the lower working class. It's called economic progress.
i was listening to the radio on the way home and heard that while it is true that folks moved up out of the middle class and also true that folks moved down out of the middle class, the ones who moved up moved way way up to the upper fringe and the ones who moved down moved way way down to the lower fringe.
(i have not had a chance to look at the actual data myself to verify)