I was on a BA flight a couple of months ago which had finished boarding but was going to be delayed for about half an hour because they were finalising some minor repairs to the aircraft; the Captain announced that we would be delayed for a while and said that we were free to use our mobiles, on the understanding that we would turn them off again as soon as he said so; it seemed to work fine.
Seems to me that Beana got someone who was having a bad day and was keen to spread the misery around (or, more charitably, perhaps was inexperienced and applying the Company's rules rigidly, without using her discretion to ask the flight deck to give permission).