Billionaire investor Warren Buffett, whose built up Berkshire Hathaway's [s:brkb] stake in Apple Inc. was asked at the conglomerate's annual meeting why he hasn't also invested in Microsoft Corp. Buffett quipped that the answer in regard to Microsoft's early years was his own "stupidity." More seriously, since Microsoft co-founder Bill Gates joined Berkshire's board, and even before, given their friendship, Berkshire has steered clear, he said. Buffett said the reason is the fear that if an acquisition or other news was announced after taking a stake, he "would be the target of suggestions, or accusations even, that [Gates] had told me something or vice versa." Buffett said his stockpickers have also been told to not buy the shares.