This is as dumb as the folks who complained about Bush for moving policy to the right.
Basic median voter agenda setting theory (specifically Cox McCubbins) explains why.
I still believe that both Obama and Bush have policy views close to the median voter. Presidential politics pushes presidents in that direction.
Congress looks like this: (you may recall my past such diagrams here)
With D representing the Democratic median (and thus the Democratic leadership). R the Republican median (and thus the Republican leadership), and m representing the country median (and roughly Obama and Bush).
Under Bush, Congress was mostly under control of R and while the president has some ability to hold policy to the middle through veto threats, in general, R will be able to pull policy to the right. We will denote policy from the Bush years as q.
In this case, Democratic leaders who get to propose the alternative under our system of government, can basically get their way, and propose something far to the left (denoted p), and Obama will go along, even though he might personally prefer something more centrist, he'd still support a far left policy over the current right leaning status quo.
Obama may wish for a policy that is more centrist, but our system of government prevents him from achieving it. (And similarly, Bush was forced into more conservative policies than he would have liked, by the same logic)
Of course, there's a lot more theory can say. For a more thorough analysis, see this article, by my classmate, Jonathan Woon.