This has been going on for a while. MSFT was the front runner followed by Yahoo and then Google entered into the fray and won. There was a time when MSFT never lost such battles.
AOL benefits by getting more ad revenues, Google made a defensive move by preventing MSFT from gaining any traction. MSFT, however, lost in many ways. Their search engine and Ad Center program continues to lag. Even worse, AOL engineers analyzed their engines and certified it to be inferior to others out there.