Pen vs. microphone
Good writer/bad talkers? This NYT article doesn't mention Ignatieff, but it's hard not to think of him and some of the observations in the previous post when you read this article. In sum, it says that good writers can be very bad conversationalists, a little lacking in people skills.
Of course, this also explains why the whole business of putting writers of any kind on TV may be misguided. (Present company included.)