The Anchoress has an exceptional take on why Katie Couric is third in the ratings:

Katie may have had high Q ratings, but she is always-and-forever the Thanksgiving Parade Girl. She’s the Olympics and Royal Weddings Girl. She is not the goto voice for information, reassurance, explanation, or gravitas.

Dan Rather, for all his faults, wrote his own copy if he needed to. He had his own voice and it was - until the last few years - a commendable, professional and credible voice. When the Challenger blew up he was appropriately solemn but still curious, informative, able to take a model of the vessel and talk intelligently with a scientist about what exactly had happened in those moments. He was intellectually spry enough to move from one element of that tragedy to another with seamlessness, gravity and maturity. He was, frankly, Rudy Giuliani on 9/11. It might have been Rather’s finest hour.

Katie could never do that. She has no “voice” of her own on the CBS Evening News because her voice - as evidenced by various ill-advised magazine articles I’ve read over the past few weeks and those blog pieces she has written which were not well vetted - is the voice of the cheerleader married and gone suburban. She cannot write her own copy, and I think that makes a world of difference to a broadcaster, because when someone is accustomed to fleshing out a story in one’s own words, one can think on one’s feet, so to speak. If the teleprompter goes awry or the story shifts quickly, one’s synapses are well-stretched and able to fire on demand, so that the whole tone of the broadcast never really dips much.

Right now, if a story shifts, Katie has a teleprompter, a voice in her ear and no freaking clue what she’s supposed to say next: enter the cheerleader. The tone becomes inconsistant, Katie looks trapped and it all starts to remind one uncomfortably of amateur night. No, I’ll go even further, it’ looks like “bloggers doing news!” And that’s pretty bad. One remembers the Challenger disaster and thinks Katie would refer to the falling rocket boosters as “Gi-normous!”