And here's the key point. Importantly, the DOJ didn't have to *legislate* to keep Microsoft out of mobile: the chilling effect of worrying about the antitrust implications slowed the company down enough to make space for others.
This is one of those "thank god some journalists understand the history of antitrust" moments. One small quibble: Allison says, "I’m not really sure Apple owes the DOJ a thank-you card for making the iPhone possible", but Gates himself noted how, distracted by antitrust, Microsoft's ability to compete in smartphones was curtailed. They might not have stopped Apple, but they might well have been able to stop Android.