He does make a good point about the uselessness of face to face debates. They generally don't accomplish anything.
They are not useless, and they do accomplish things.
In this case, what was accomplished was that viewers were persuaded as to the strength of Ron Paul's positions and the weakness of Krugman's. Krugman's arguments were weak and poorly made; he barely even presented his case at all. He instead reverted very early to obfuscation: just throw around a bunch of random educated-sounding gobbledegook and terminology and obscure historical references and then sit back as everyone defers to your erudition in gape-mouthed awe. That's what he did when the interviewer asked him what the right number was or whatever.
Unfortunately for him, Paul matched him and then some. He understood, and extremely thoroughly, every random reference and Greenspan-babble that Krugman spewed forth. Paul's comments and demeanor made it clear that he understood, and Krugman came off as a know-it-all that had finally met someone who knew much more than him and could call him on his bogus points that usually everyone has no choice but to accept because they don't know anything about it. This type of person is called in the modern vernacular a "poser" I understand. It's always nice to see a poser smacked down by someone who's the real deal. The WWII example, in fact, was the example brought up by Krugman! Paul brought up the facts of the matter and used his own historical episode against him. Every major point Krugman made was addressed by Paul, on the other hand there were several major points which Paul presented or appeared to win decisively, and then Krugman just left them that way, making no attempt at rejoinder. The WWII example, for instance, he just left it hanging there, he never had a "come-back" explaining Paul was wrong.
All in all it was not a completely one-sided debate, it was a good debate, but Paul was the clear victor. I think any Forensics coach would agree. Krugman was just sad. He started off not too bad, but really deteriorated as it went on.
Debate is always for persuading the spectator, not your opponent. Ron Paul does that. Does it well. How many people have come into the liberty movement because of Ron Paul's appearances in debates?