Why hasn't Obama championed his own economic philosophy rather than parroting that of the Republicans?

According to the Washington Post,

Obama said that just as people and companies have had to be cautious about spending, "government should have to tighten its belt as well. We need to do it in an intelligent way. We need to make sure we do things smarter, rather than just lopping something off arbitrarily without having thought it through."

As Paul Krugman pointed out,

We’ll never know how differently the politics would have played if Obama, instead of systematically echoing and giving credibility to all the arguments of the people who want to destroy him, had actually stood up for a different economic philosophy. But we do know how his actual strategy has worked, and it hasn’t been a success.

That's one reason Obama's supporters are so angry with him. He simply hasn't stood up for what he said he believes—or at least what he led many of to think he believes. It's one thing to seek conciliation with the other side; it's another never to argue for what you believe.