Investors undertook their annual pilgrimage to Omaha this weekend to hear Warren Buffett opine on markets and the world. One surprise is that the Berkshire Hathaway CEO seems to have adapted his famous Buffett Rule of taxation when it applies to his own company.

Readers may recall the original Buffett Rule that President Obama offered as part of his re-election campaign that essentially posited a minimum tax rate for the rich of about 30%. Mr. Buffett heartily endorsed the idea and Mr. Obama hauled out St. Warren as a soak-the-rich...