On Condition of Anonymity

There's something funny about this line. The article concerns a growing sense among Republicans that Sarah Palin is a disaster. But then there's this strange line:

Asked about Palin's performance in the CBS interview, a McCain official briefing reporters on condition of anonymity said: "She did fine. She's a tremendous asset and a fantastic candidate."

A McCain official needs to have the condition of anonymity to say Palin did fine, that she's a tremendous asset and a fantastic candidate? Wouldn't that basically be their constant claim? Something they could say quite openly?