I may be totally ignorant here, but why isn't Robert Novak who actually wrote the article that "outed" Valerie Plame, being forced to testify to HIS source?
If one first assumes the investigators know what they are doing THEN one might deduce they already know Novak's source and have determined no 'foul' to either the source and Novak -further that it has been confirmed that the source he/she/it was not the source for these other reporters. Hence, either there is a source yet to be revealed and investigated OR these other reporters are liars...
Novak has probably already done that.
Perhaps he has. But the investigation has moved on to bigger and better things.
Though the MSM has been loathe to admit it -- this article being a prime example -- the scope of this grand jury investigation goes far beyond the Plame Affair.
The GJ is actually investigating the entire nexus of unauthorized leaks from and about the CIA, many of which had national security implications.
The media is not thrilled by this development, as they have assiduously cultivated these leaks in order to serve their anti-Bush political agenda. Thus, we see the odd situation where the media is keeping their reporting low-key and practicing damage control over a "freedom of the press" issue they would normally be screaming from the rooftops.
He's next!