Chris Anderson said that it's mostly the second-rate stuff that doesn't get published, even over time. There must have been a handful of talks that were really disappointing and they don't seem to want them making the rounds.
Is there a list of ones they plan on posting? I was under the impression they were only posting 1 every weekday, and so far the only 2 up (at least on the official site) are Blaise Aguera y Arcas on Augmented Reality and Jamie Oliver's wish for food for every child.
While I found both of those interesting, I'm really looking forward to a few of the others and only 1/day being posted is brutal.