August 17, 2010; Source: | So far some 40 billionaires have answered the call from Warren Buffett and Bill Gates to donate at least half their wealth to charity.  While that might appear to be an impressive response, suggests that number could be a lot larger, considering there are some 1,000 billionaires in the world.

Who are the holdouts and why haven’t they signed the Giving Pledge?  This article answers that question in a few cases. One very wealthy person who might have been on the list from the start had Messrs. Gates and Buffett not forgotten to ask him is Wall Street tycoon Carl Icahn.  However, being a forgiving sort, Icahn, who has a personal fortune worth $10.5 billion, says he’s eager to sign on to the campaign.

Other well-known ultra wealthy individuals not on the list include George Soros, Meg Whitman, and Oprah Winfrey. Financialedge says it’s not clear if Soros will take part in the campaign—or that it matters much if he doesn’t. “Soros has given away $7 billion dollars of his fortune to charitable endeavors already and he plans to donate a large portion of his total wealth anyway.”

Ebay founder Meg Whitman, who also didn’t get a personal invitation to take part, said even if she does hear from Gates and Buffett, she’ll decline. Whitman, who is running for governor of California, is planning her own charitable foundation.  Winfrey, who holds the distinction of being the world’s richest woman, hasn’t made her intentions known yet about the Giving Pledge or what she ultimately plans to do with her fortune, currently valued a $2.4 billion.  Then again, maybe the reluctance of some of these billionaires is like the old Groucho Marx line, “I don’t care to belong to any club that will have me as a member.”—Bruce Trachtenberg