It's not his impressive track record. It's because he never passes the buck (pun intended):

It’s my job to keep Berkshire far away from problems [related to leverage and undue risk]. Charlie and I believe that a CEO must not delegate risk control. It’s simply too important. At Berkshire, I both initiate and monitor every derivatives contract on our books, with the exception of operations-related contracts at a few of our subsidiaries, such as MidAmerican, and the minor runoff contracts at General Re. If Berkshire ever gets in trouble, it will be my fault. It will not be because of misjudgments made by a Risk Committee or Chief Risk Officer.