All I can say is.... wow....
http://news.yahoo.com/six-waltons-more-wealth-bottom-30-americans-182819449.html
Different people will take this different ways, but Jeffrey Goldberg tells us that six members of the Walton family (the original owners of WalMart) have more wealth than the bottom 30 % of Americans. Here's where he says it:
In 2007, according to the labor economist Sylvia Allegretto , the six Walton family members on the Forbes 400 had a net worth equal to the bottom 30 percent of all Americans.
And given that he quotes us here at Forbes on the point, he's almost certainly right.