Most companies have been on a buying spree. Yahoo bought flickr. Ask Jeeves bought bloglines. A long time ago, Google bought blogger.
Do you see something missing here? Where is Microsoft? Why are Microsoft bidding their time, working inhouse to develop technology slowly instead of acquiring companies in order to be competitive faster. Maybe a couple of things have made them think that they can bide their time. Let the market settle. Let Yahoo and Google duke it out. And in the meantime, no antitrust pressure on Microsoft either.
I guess they have the money, and money is time.