Whether the president, vice-president, or Libby were legally entitled to leak the information is not the key issue here. It's a distraction.
In 2003 a CIA officer was outed in the media. An investigation was authorized to determine the facts of the matter. It was agreed at that time, by the White House as well as others, that this was a serious matter and that it was important to get to the bottom of who did what.
At that time people at the White House were claiming to have had no involvement in the matter. Whether they were weaseling and actually meant that (in their opinions) they had no criminal involvement is irrelevant. The point is that, in order to determine the facts of the matter, Fitzgerald needed to talk to people who had knowledge of the leak and needed to find out what they knew. And instead of cooperating with the investigation the people at the White House stalled, delayed, evaded, and dissembled.
Some of them -- notably Scooter Libby -- made statements to the investigators and testimony to the Grand Jury which turned out to be significantly false. That is what Libby is charged with -- making false and misleading statements which have hindered the investigation.
It is very difficult to know who is guilty of what if people lie to investigators or otherwise obstruct the investigation. And if investigators cannot determine who to charge and what to charge them with, then criminals walk free. That's why obstruction of justice is a serious matter.
It is nice if Libby is now telling the truth about how Valerie Wilson's name got leaked and her cover blown. If this is indeed the truth, it may help Fitzgerald get to the bottom of that matter and determine whether criminal charges are warranted (and if so which ones, and against whom). But that doesn't alter the fact that for the past couple of years Libby and others appear to have willfully tried to stymie Fitzgerald's investigation.
It is becoming increasingly clear that Libby did indeed have knowledge about how Valerie Wilson came to be outed -- that he had information pertinent to the investigation of that outing, and that instead of cooperating with the investigation as he was legally required to do he chose to conceal what he knew and to muddy the investigative waters. And his latest statements serve as one more confirmation of that increasingly obvious fact.
That is what Libby is charged with. That is what he is going to be tried for. And so far his defense seems to be one attempt after another to distract attention from that basic fact.