Maybe we could have smaller pins if the plugs locked into place, sorta like phone sockets do. As Bumblethumper said, some sockets have shutters so having shallower pin holes wouldn't mean a problem with accidentally touching the contacts inside the socket. Most sockets have on/off switches on them anyway now, but perhaps there could be a mechanism inside the socket which tells it if a plug is inserted and if not then the socket doesn't even get power until there is.