Whether under Warren Buffett or now under Greg Abel, Berkshire Hathaway's (BRKA +1.36%) (BRKB +1.43%) stock portfolio has always operated with a concentrated approach: When the team sees a stock they really like, they load up. Buffett has always believed that diversification is an excuse for ignorance, and while he understands that most general investors use the practice, it's not something the Oracle of Omaha has ever deployed. Abel has no intention of departing from the concentrated approach in Berkshire' ...