The letter was entirely polite and businesslike, but something about it chilled Wilhelm Zeller, chairman of one of the world's largest insurance companies. Moody's Investors Service wanted to inform Zeller's firm the giant German insurer Hannover Re, that it had decided to rate its financial health at no charge. But the letter went on to suggest that Moody's looked forward to the day Hannover would be willing to pay. In the margin of the letter, Zeller scribbled an urgent note to his finance chief: "Hier besteht handlungsbedarf." We need to act. Hannover, which was already writing six-figure checks annually to...