Warren Buffett has regularly endorsed a low-cost S&P 500 index fund as the best option for non-professional investors that want exposure to U.S. stocks. Consequently, his decision to sell Berkshire's S&P 500 index funds begs the question: Has Buffett lost confidence in the U.S. stock market or the American economy?

Warren Buffett, the CEO of Berkshire Hathaway, oversees a $298 billion portfolio of publicly traded stocks and securities, besides numerous wholly owned subsidiaries. Berkshire is also sitting on $325 billion in cash,