Not sure how this is all going to play out, but Novak had two sources and it looks like they were Libby and Rove, but Libby may have been the leaking source and Rove the confirming source. That really put Libby in a hotter seat because Rove can say he didn't reveal Plame's ID. Of course, the indictments are not about revealing the ID but perjury and obstruction of justice. Perhaps Rove told all under oath when it really counted, but Libby fudged, especially understandable if Libby were the original leaking source.
Or it's still possible that Rove will be put on the hotseat soon.
What seems true though is that Libby must have presented an easier target.