I have read in the "NY times magazine - the college issue," that over 80% of students in top universities across the nation are upper middle class and higher on the social ladder. So what you speak of Lindbergh is the case.
Maybe something to do with the fact that they received better education initially & understand its value. i.e. They can pay for it & will work for it. AA helps the former, but the latter, well I've met a host of poor people who would rather work physically 12hrs/day than put that same time into an education & its delayed gratification.