I think the UK made the on/off switches a requirement a long while back.
As regarding the sockets and lightswitches in bathrooms, an electrician told me that
if there's water on the socket or on your hand or whatever then you could risk receiving a 240V
current just by touching the switch.
I think it's just a case of the UK being a bit overcautious, but they do reckon the extra voltage could
make a difference between life or death. Obviously, if you're in the bathtub and an electrical appliance that is
on falls in you're toast whether you're in the UK or US but the more incidental shocks from sockets and switches
may be the difference.
Strangely, it seems that the 240V shaver sockets are ok, so if you plugged in the shaver and then stuck it
in the bathtub (full of water) you'd think that'd be just as much a hazard...
Matt