Well, the inconceivable, it seems, has now been conceived (as seems to be true of so much about the Obama era so far). And one reason might be that Obama has said that, to a point, he'll let Gates be Gates.
It would be a mistake to regard Gates as merely a holdover from the Bush administration. Literally, of course, he is. But since coming to the Pentagon in December 2006, he has altered the dynamics of decision-making and, as a result, of policy.
Before Gates, the National Security Council was dysfunctional. Rumsfeld would skip meetings and refuse to let his deputies speak on his behalf. His tag-team partner, Vice President Dick Cheney, would block the NSC from forming a consensus on issues that concerned him; instead he would meet alone with President Bush afterward, a practice that compelled the secretary of state—Colin Powell in the first term, Condoleezza Rice in the second—to go around the process as well.
When Gates came onboard, he demanded high-level meetings, with all the players present, debating their positions all at once before the president, with a decision made at the end. Some officials contend that it is because of Gates that U.S. troops are coming out of Iraq a bit more rapidly than they might have otherwise—and that Bush hasn't bombed Iran.
At the same time, it would be a mistake to infer from all this that Gates will take his reappointment as a mandate for autonomy—a permission slip to do whatever he wants without political interference. First, if it's true that retired Gen. Jim Jones will be Obama's national security adviser, this is going to be a very tightly run NSC. All impulses toward freelancing, from Gates or anybody else (including Hillary Clinton, if she's secretary of state), will be firmly reined in. (More on Jones later, if he's announced.)
Second, and more to the point, Gates is not the freelancing type. Though hardly a passive servant, he spent most of his career as a staff officer. Even as secretary of defense, he has constantly been aware—and has emphasized many times, in public and private—that the president is the decider. At age 65, Gates is not so old, but he is very much of the "old school" when it comes to loyalty and lines of authority.
At Obama's press conference today, a reporter asked him how he reconciled his campaign promise of change and new vision with his appointment of so many Washington insiders. Obama replied: "Understand where the vision for change comes from first and foremost—it comes from me. … My job is to provide a vision of where we are going and to make sure my team is implementing it." He added that his aides had to be smart enough to advise him on that vision and experienced enough—knowledgeable enough about the way Washington works—to put it into effect.
By that standard, Robert Gates is an excellent choice.