Without sounding disgusting; you have to take into account these are used for people of all ages, some of which are incontinent. They have fail safes, a lot now also are machine washable!
Boxy, electric blankets nowadays have so many safety backups. You can't leave one on all nights constantly even if you wanted to. Whilst married I had to suffer the pain of waking up every 2 hours to turn my wife's back on - otherwise she'd kick me a few times to tell me it had turned off. I can happy sleep outside on the roof, even in this weather... I don't do 'warm'!
When I say you can't leave one on all night, I mean you can't leave one on all night on full whack. You'd probably end up dehydrating. Most are 12-36V if I remember correctly. As gingejbee said, they aren't running on 240v or 110v.
gingejbee: You don't need to apologise, I didn't really word it right anyway. Your answer was far more precise than mine. As long as wolf gets the answer they're looking for then I'm happy :)
I have had a chat with Frankie about this and we have decided to give it a trial run once it gets really cold. Will also try and convince princess Stupid that it is a good idea to keep warm.