So why isn't Russert indicted for contradicting Libby?
Probably because the prosecutor has the testimony of numerous individuals (Ari Fleishcer, the Vice President, Karl Rove, the Under Secretary of State) who discussed Plame with Libby before he ever talked to Russert, thus contradicting the testimony of Libby but not that of Russert.
Because he is the media, and he is a democrat. Next question
Because he did not, Libby he alleges called him as an upset viewer over something he had just seen on MSNBC and complained about a commentator. Russett said he would pass it on but why not call his bossess. Libby upset then asked if Tim knew of a Valerie Plame. Russett said he did not. Russett relayed this "upset viewer" at " a high level " then left on vacation to return to hear the buzz over the Wilson/Plame story written by Novak. Tim then said it hit him he was on the list of those Libby called and put two and two together. What upset Libby the possible "straw man" to make calls in the first place? Libby is loyal to whom ever he is working under and Tim Russett whether we like all he has to say is also considered a man of integrity. You would not want Russett on the stand contradicting what you had testified to.
Something happened to rattle Libby coming off from MSNBC to cause him to make the call complaining about a commentator, unless it was a bogus lead in complaint and I would not hope that Libby would intentionally do such a thing. Remember Libby was loyal to all those he has worked under or for-mention is made of that in the testimony for Marc Rich's innocence and end result his pardon.