I'd argue it's more comfort that you can be reached or reach someone than actual safety. But I don't really disagree with your broader point. This system doesn't seem very practical for a whole range of issues.

Plenty of other live events have policies against recording and cell phone use and don't seem to have any serious problems enforcing those policies (or, indeed, need to do much "enforcement" at all). Perhaps rock concerts are different because of the type of crowd.