Well why it has to be more? See, if that was 20%, it meant that wealth distribution is entirely random and parents can't do anything to help their children succ

Well why it has to be more? See, if that was 20%, it meant that wealth distribution is entirely random and parents can't do anything to help their children succeed - that is not the world where many want to live. There should be a balance - getting from poor to rich must be possible, but hard. People who get rich are those to work towards distant goals and accept delayed gratification. If they are unable to pass anything at all to their children they'd have a much better time drinking and smoking hash - there isn't so much they can spend in their lifetimes anyway, and if they can't pass anything (even cultural! that helps besides money and would already skew that ratio away from 20% down, even if all money was taken away) to their kids - why bother? To me, 7% of 20% poorest making it to 20% richest sounds already too much.