> It's impossible to conclude from the evidence presented that the antitrust action had no effect on the breaking down of Microsoft's monopoly. It's entirely plausible that the enforcement left them unable to respond as quickly to new markets as their competitors, leading to them beginning to get undermined a few years later.

In fact, companies targeted by antitrust (I think it was IBM) have stated that antitrust regulation, by itself, shifted their focus. You are no longer rushing ahead, instead you must be cautious about everything. So it is indeed quite plausible that antitrust actions against Microsoft made possible the current non-Microsoft-dominated era.