Why Is Novak Skating on Rove/Plame Affair?

One of the dangers inherent in jailing journalists for not disclosing confidential sources, is that this draconian punishment can be invoked selectively against targeted journalists. Two excellent and independent reporters may go to jail while Robert Novak has not -- to my knowledge -- been presented with the tragic choice of disclosure or imprisonment. Why has he been exempted? Is it because he toes the administration's line? Is it because he knows whether Karl Rove was the source? An explanation for this apparent double standard is called for!

UPDATE

After I wrote this, Robert Kuttner published an op ed piece in The Boston Globe making a similar point in greater detail. I urge readers to access the Kuttner article.