To be honest I think the chewing gum rule is a bit of damage limitation, too many people pursue venues for the cleaning, replacement costs of chewing gum on clothing.
I'd quite happily ban cameras from all venues, and have a zero tolerance policy on people taking pictures with mobile phones. I'm fed up with going to gigs only to have to watch that gig through the screens of other peoples cameras and phones, and don't get me started on being blinded by constant flash photography.