"We have dedicated considerable time and resources to an analysis of a potential transaction and are confident that the combination will receive all necessary regulatory approvals." Uh, really?
If the biggest advertising entity on the web (Google) can buy one of the other biggest advertising entities (Doubleclick), I'm pretty sure one of the also-rans can buy another also-ran.
Also, much of Google's "monopoly" comes from a source that is heavily protected by law: the pagerank patent. Patents are government granted monopolies with limited time; as such, there is little or no legal recourse as any mildly abusive behaviour is expected, tolerated, and what the system was designed to provide.