The missing billionaires

????The level of giving varies -- Oracle's (ORCL, Fortune 500) Ellison pledges to give away "at least 95%" of his wealth, while Ron Perelman leaves it a bit more vague, pledging "up to half my assets ... after my family and children have been provided for." The Giving Pledge did not return telephone calls and e-mails seeking clarity on the 50% minimum and Perelman's pledge.

????Buffett says the campaign to get more of America's richest to give up their wealth continues, though not always smoothly. Some billionaires approached by the country's two richest men have already rejected the idea. Buffett wouldn't name names, but says that general dissatisfaction with the government played a role for some. (He says he frequently got a political lecture from those billionaires after making his request.) Others believed in keeping the money in the family, what Buffett calls "a fairly dynastic view of wealth." And some "just had a plane to catch."