ZDNet: Story: Triumph of the Bill: Why Microsoft won "...American antitrust laws were designed to protect consumers from obviously predatory business tactics. They weren't designed to protect consumers from a single company. And they weren't designed to protect other businesses or to preserve competition--at least not in the abstract sense of, "What would competition be like today if Microsoft hadn't done X?""
This is a key point: antitrust is about protecting consumers, not competitors.