At Defcon, but not at Black Hat (the more important of the two), where Keith Alexander gave a keynote.

Not just any keynote either, it was more or less pro-government propaganda, complete with pre-vetted questions from the audience.

Also happened during the sequester, and when GSA had recently gotten in trouble for Vegas boondoggles, so I think there was a reduction in interest/increase in cancellations, and this was both a cheap way to send a "message", and a face-saving way to help them cancel.