Matt Yglesias points out that tonight's debate may be a “Town Hall,” but moderator Tom Brokaw, not the audience, will pick the questions:

In essence, Tom Brokaw and his staff will be asking the questions. They're sifting through a big group of people, and their pre-set questions, and picking the questions they like. Meanwhile, though, Brokaw and co. get to evade responsibility for the questions if people don't like them — it was real people asking! And no followups, so if John McCain gets a question about his plan to cut Medicare and wants to give an answer about Bill Ayers, nobody can stop him.

Remember: Brokaw was the McCain camp's choice to moderate this debate -- and is NBC's liaison to the GOP candidate.