The Buffetts and Gateses started it, and then other names followed: Zuckerberg. Bloomberg. Rockefeller.
Over the past decade, many of the world’s richest people have made the Giving Pledge — a promise that they will give a majority of their wealth to charity.
But it’s a club that members of the richest family in America, the descendants of Wal-Mart Stores founder Sam Walton and his wife, Helen, have decided not to join.