Warren Buffett has famously referred to iPhone maker Apple (AAPL) as "probably the best business I know in the world." It's long been one of Buffett's favorite stocks, and it has been a staple in the Berkshire Hathaway (BRK.A -0.16%) (BRK.B -0.13%) portfolio for years.But while it still remains the top holding in the portfolio, it may not stay in that position for much longer. Here's why that could happen and what it might mean for investors. Apple is no longer far and away the biggest Buffett holdingIt was ...