The Economist has an article about this subject, too: "But a new paper by Jose Azar, Martin Schmalz and Isabel Tecu argues that trustbusters now need to look i

The Economist has an article about this subject, too: "But a new paper by Jose Azar, Martin Schmalz and Isabel Tecu argues that trustbusters now need to look in a new direction: at concentrated ownership. If, for instance, a mutual fund owns shares in two rival companies in the same industry, it would not be in their best interest as shareholders to encourage them to act in a competitive way. The boss of Delta Airlines might propose a price war to boost his business. But would a mutual-fund manager who also owned shares in United Airlines be supportive? And would company managements be as keen to cut prices and fight for market share if they knew that their shareholders did not want them to? Mssrs Azar, Schmalz and Tecu find evidence for exactly this in the airline industry. Including levels of common ownership in conventional measures drastically increases market concentration to more than ten times the level authorities say would be "likely to enhance market power"." Bottom line: it looks like there should be competition, but maybe there isn't due to ownership structures.