Let me just ask this, considering that many tablets have data plans (I understand that they are optional to get, but still) what's to already stop someone from pulling out their Ipad? I have seen people use their Ipads/tablets at shows before.
Furthermore, I can understand the whole issue with wanting to use wifi over wanting to use data. Using data costs the user money, however, if you were to use wifi it's free. Personally, if I were at a starbucks or somewhere else (where it is okay to use my phone) and wifi is an option, I almost always turn it on and use it rather then having to pay for data. Sure, using data doesn't cost me a huge super amount, but a little bit does add up over time. So, if I can save here and there I would.
"If you try to shag my husband while I am still alive, I will shove the art of motorcycle maintenance up your rancid little Cu**. That's a good dear"
Tom Stoppard's Rock N Roll