Common sense is all the link you need. Extreme wealth, like the Hearst, Getty, Rockefeller, Carnegie, Kennedy type Wealth does tend to stay around for generations.
Well...there you have it, forum. Next time Guesser challenges anything you say, all you need to respond is "it's simply common sense." You're confusing family connections with opportunity. A bum who lives under a bridge has the same opportunity as a Kennedy or Carnegie or Melon to do something with himself.
The majority of families you listed above...we're only in what, generation No. 3? I wish I could find a link I posted in here some years ago, but high wealth only tends to stay within a family for 5-6 generations on average. Not to mention, not all of the businessmen you listed were born into wealth. Go far back enough into history, and someone in the family wasn't very well to do...yet made something of themselves.