This read much more like an advertisement for GreaterThanZero's services than an article whose conclusion actually addresses the title's question, but the author seemed to do a good job accounting for the differences between Warren Buffet's estate and a regular, living person's money (namely that the person sometimes needs to spend it).

Actually, come to think of it, I don't think the author explained why Buffet's estate should be treated as if withdrawals will never be made from it, but I assume it's because the 10% of his money that will go into short term savings bonds is still a ridiculous amount of money and should be sufficient to cover any expenses in the foreseeable future.