Even my alma mater is on the list, I really dislike this sort of ranking because of what Alexandre pointed out. According to some studies, US is among the worst in social mobility in the developed world. Also, any earnings ranking is going to be unfair to schools with a large fraction of students majoring in arts, music, education, theater, etc and advantageous to schools with larger proportion of students in, say, finance or engineering.
At Northwestern, fresh grads from its engineering school earn much more (twice) than those from music school and communication school. Yet, they are all NU grads.