I doubt they feel honor bound to protect a source that supplied forged documents.
I realize "honor" is not the right word to use when dealing with the dims and msm.
I bet if someone, say Killian's widow, were to file a slander suit, the first setp in discovery would be a sub poena for their source. And I bet they would have no defense against it.
Of course this wouldn't happen until after the election, but I bet a re-elected Bush administration could make things pretty hot for CBS if they wanted to, and they would have good reason to.
My bet is that CBS coughs up the name voluntarily to avoid all sorts of unpleasantness and credibility problems.