My initial reaction to Clinton's appointment was that Obama already understands he won but 52/48% of the national vote - going downhill, with the wind behind him, after 8 years of Bush, with 4 times as much money raised as Bush, fighting 2 unpopular wars and the worst depression of the capitalist era looming larger each week. Not exacly a landslide.
First thing - he needs to get re-elected. Hence Gates at Defense and Clinton - she has to appeal to all her Democrats in key States who wouldn't vote for him.