The Debate That Was Not.

As Kathleen Jamieson put it well on Bill Moyers Journal, the Biden-Palin did not change a whole of things, why? Because it was not a debate but a discourse:

There's no way to win or lose 90 minutes of discourse. You can win an argument.
You can win a chess game. You can win a football game. You can't win 90 minutes
of discourse.

(.../...)

Is that a problem? Well, not if you're watching a game but it may be a different story if you want to assess someone's competence for VP.

The reason that the format matters is that in a format in which you have a short answer, no follow up, no exchange between candidates if a candidate has one layer of information and doesn't have the ability to follow up and follow up and follow up with depth, you don't know that.
That's the format that was not the format that was problematic for Governor Palin when she was interviewed by Katie Couric. Katie Couric's questions and then Governor Palin's problematic answers came largely in the second and third follow ups. And so, the format matters, because it let Governor Palin feature a strength without testing what is a potential weakness.
If you wanted to ask not who won and who lost, but who was qualified to be the next president of the United States in unanticipated circumstances for that question to be answered, you need a more open format with more follow ups and more direct exchange.