Fly On The Wall explains:
Keeping Bob Gates as Secretary of Defense was the most dramatic signal Barack Obama could have sent that he intends to implement major changes in defense policy. That may sound counterintuitive, but it has the virtue of being true.
As Josh noted this morning, "cabinet appointees execute policy. They work for the president." So if Gates is tasked to take us out of Iraq and to redouble our efforts in Afghanistan, we can expect him to carry out both tasks with the same degree of competence he's exhibited thus far in his tenure. In a properly functioning administration, the Secretary of Defense is one of several key voices advising the president on where and how to exercise military force. But he possesses primary responsibility for deciding how that force should be structured, staffed, equipped, and supplied. Those are decisions the president largely delegates, and thus where the secretary exercises his greatest degree of autonomy. And it is in those realms of defense policy that Gates has most distinguished himself. In retaining Gates, Obama is sending a clear signal to the Pentagon bureaucracy that their usual strategy of stalling and out-lasting civilian appointees is going to fail; that he intends to pursue Gates' key reforms. And that's a decision which should make us all stand and cheer."