The Nobel folks decided, rightly or wrongly, to send the message that the United States as a country is important, and the Obama leadership is welcomed, and the Bush leadership is rebuked in a major way.
The Obama White House was so surprised by this whole thing that I find it surprising the President could make a statement within hours.
Should he have declined the honor? Reasonable people can argue yes and no around that. For me, he described the prize as a call to action. A call to action cannot be argued, prize or not.