Those appear to be a list of anecdotes as opposed to a real analysis of who becomes wealthy and the means of their families in America. Unfortunately, I'm not familiar enough with the social science literature to fix the reference problem, but at least from the survey work presented in "The Millionaire Next Door", many of the wealthy American surveyed there did not appear to be from family money.
Not true. Society nowadays in the US is actually relatively immobile, compared to the 19th century.
http://en.wikipedia.org/wiki/List_of_wealthiest_historical_f...
http://en.wikipedia.org/wiki/Andrew_Carnegie
http://en.wikipedia.org/wiki/Henry_Ford
http://en.wikipedia.org/wiki/Cornelius_Vanderbilt
http://en.wikipedia.org/wiki/John_D._Rockefeller
http://en.wikipedia.org/wiki/John_Jacob_Astor
All five were from poor/middle class backgrounds. Compare to Bill Gates, whose father was a name partner in the largest law firm in Seattle, Preston, Gates & Ellis, and whose mother knew the CEO of IBM.