I think Ben Smith gets this exactly right:
Bill Clinton, former aides say, worked hard for his Cabinet that "looks like America," and reached outside the normal establishment channels for some of his picks. George W. Bush, reaching into a less diverse GOP, did the same in some cases.
Sixteen years later, Obama hasn't had make any apparent special effort to avoid having a cabinet dominated by white guys: People like Susan Rice, Steven Chu, Eric Shinseki, Hillary Clinton, Bill Richardson, Janet Napolitano, and Eric Holder are obvious choices, with their own power bases, relationships with Obama, and/or establishment credentials -- some earned at high levels of the Clinton administration -- that the notion of a special effort to ensure diversity at the top level of this administration seems sort of irrelevant.
It's true. All of the appointees Smith lists are minorities or women, but they are so accomplished and talented that no one has dared called them affirmative action picks. They mirror Obama in that way.
In my short article on things Bush got right (did I mention it's a short article?), I noted that Bush put together the most diverse executive branch team in history. Obama's will rival his but may not top it. The important point, though, is that Bush's cabinet secretaries and aides performed so poorly that it almost felt like W. was making a high-stakes argument against affirmative action. He didn't know it, but in actuality he was making a high-stakes argument against prioritizing loyalty over competence. See Gonzales and Miers in that regard.