From one of the Washington Post's stories about WikiLeaks:
A senior U.S. intelligence officer, speaking on the condition of anonymity because he was not authorized to be identified, said: "No one should think of American diplomats as spies. But our diplomats do, in fact, help add to our country's body of knowledge on a wide range of important issues. That's logical and entirely appropriate, and they do so in strict accord with American law."
The source is anonymous because he must remain…anonymous. Got it.