From Microsoft viewpoint, 30% share of the search market is a hell of a lot more than the less than 10% they have at the moment and who knows, if they combine technologies Yahoo developed over the years with Windows and other resources, they may be able to gain another 5-10% of the market.

One other thing Balmer said which I believe is that, they usually get into new market late, but they always succeeds, XBox for example, it was only developed years and years after Playstation and others have dominated the games market but look what Microsoft has turn Xbox to today.