First, he's not being charged with leaking info. However, even if you have classified info...if it becomes public you can talk about it (in regards to the public article).
For example, the Chinese Spies we just caught. Intel officers knew about this before it hit the newpapers. They can't talk about it. Once it's out they can talk about what was in the paper, but can't comment on if it's accurate or if there's more/less there that meets the eye.
What I am saying is that Fitz might say Libby should ought to have told investigators how he got Plame's information through the CIA etc. and not from a reporter. It goes to obstruction of justice etc.
But don't get me wrong here! What Woodward did was huge and I really think Libby got wacked in public for no good reason. If I was Libby and managed to have the charges dropped I would sue the government for a malicious prosecution.