You can't turn everything electronic off - pacemakers, for instance! Even modern pacemakers with radios inside. They will, in the event of what is called a 'Medical Event Emergency' start transmitting. The power level is very low, though only 25 microwatts. Hearing aids are interesting,because latest technology hearing aids are also using radio transmitters. The power levels are low enough that the CAA aren't worried - I have an official email confirming that. It's more dangerous, I would have thought, to have a passenger who can't hear instructions. Watches are of such low power that they aren't covered by the US FCC Part 15 rules - I'm not sure about European EMC rules.
Then there's other interesting electronic medical devices that you really want to keep going, such as insulin pumps, sphincter controllers, nerve stimulators for controlling Parkinson's disease and the like.
One of these areas where it needs a bit of common sense to be applied. But as more personal medical devices incorporate radio, it could be a perception rather than a physical problem.