I think the explanation is much simpler. Some (a minority) of electronic devices have WiFi or telephone capabilities. It is impossible for the cc to ask every passenger whether or not his/her device has such capability and if they have it switched off. Therefore in the 'better safe than sorry' category it is far simpler to ban the use of all electronic devices. No need to identify anything other than an electronic device in use. I believe the biggest problem with these devices is that they can interfere with cockpit communication. Like the interference you hear when you place them next to a speaker.

When it became slightly ridiculous was when a KLM FA made a very big deal about me using a camera during landing. I did what she asked but only after a slight protest...