This had never occurred to me! Sometimes they're right, actually, and the questions can be someone showing off their knowledge, trying to catch out the presenter, off topic, or just plain dumb. But since that Q&A often is the only interactivity we have in sessions, we need to think about this. I'd be curious if PCMA breakout session leaders get a bunch of IMs or e-mails later from those who didn't want to ask in person? I know if I think my question is questionable, I try to ask the presenter afterward in private. Is this really any different because it's a little further off in time and distance? I'm not sure, but it's chewy food for thought.
As is this morsel from Jamie: "notice that the younger generation did not assume that learning required a group of people to be having a synchronous conversation in person. In fact, they thought it was "rude" to make people learn that way (I'm extrapolating a bit here, but you see my point)."
Update: Check out this post full of tips on how to get people "talking" during a webinar (thanks for another great post, Ken!). While most are very specific to the online environment, this last tip applies to face-to-face presenters as well, I think: