Can it really be bad to be so good? Consider the case of Frito-Lay, which has long been America's king of salty snacks. In recent years the PepsiCo subsidiary, whose bite-size best sellers range from Lay's Potato Chips to Rold Gold Pretzels, has crunched more than one rival that got hungry for its business. Since the late 1980s, Frito-Lay, with $5.5 billion in sales last year, has boosted its industry market share from 38% to a towering 55%.
But despite--or because of--this stellar performance, Washington suspects that something must be rancid at Frito-Lay. In a move that caught even antitrust experts...