At least NPR had Fred Kaplan on awhile back to explain (from Dec. 21):
Mr. KAPLAN: Right. He wrote an article in the December 4th issue of Weekly Standards - the briefing is dated December 17th, I believe. He did a calculation which showed that you would need 80,000 additional U.S. troops. He then said, persuasively, that you could probably cut that down to 50,000. And then in this briefing, he's all of the sudden got 21,000 without any explanation for the difference, and as far as I can tell, no difference in the analysis. It's unclear how many troops are really needed for this plan.
Of course, that didn't stop them from having Kagan on on Jan. 11 to tell us:
Dr. KAGAN: You know, in the report that we did and published a little while ago, we recommended an increase of five American army brigade combat teams into Baghdad in addition to the five that are already there. And we do believe that such a doubling of the force that we have now in Baghdad can be decisive, especially if it is coupled with an influx of additional Iraqi forces to assist.
Frankly, I think that it's possible for us to succeed with this force level that the president is announcing, even if a number of those Iraqi forces don't show up. And so I think this is a plan that does - just looking at this general outline - have a good prospect for success.
Nothing keeps these people off the rolodex.