You overestimate the phasability of the average person, I think. Especially in places with geek-based convention centres.
Plus, the camera might not have been obvious; if there's an obvious camera, people are more likely to *mug for it.
* Ah, English. In this slang usage, "mug" means "to play-act, in an amateur, untrained manner, as if before an audience."
* Also, "mug" used to mean "face". Hence, "mug-shot", or "a picture of someone's face."