The quick answer is that he is paying taxes on long term capital gains which are taxed at a flat but lower rate than the marginal tax rate of higher earners. However, it is important to understand that he does indeed do everything he can to limit the taxes paid by those businesses in the Berkshire portfolio. As Gusser said, he owes years of back taxes and continues to contest those taxes. Further, he uses government to build competitive advantage. He actively lobbies for additional regulations that are specifically geared toward providing him advantage. Basically, he throws up barriers to competition through government regulations. He has used government as an anticompetitive weapon for years.
The more you know about Buffet, the more you realize he is a hypocrite and a fraud. Rich yes, honorable, absolutely not.