In the event that an element would leak current into the liquid, the whole kettle itself would also be live.. and your bound to touch it eventually causing the same issue as using the metal spoon... so if you ask me, the idea is to ensure that the kettle and liquid doesn't get charged in the first place...
GFCI as porcupine73 stated is the best way to prevent that...
I also have the whole kettle grounded, so if the liquid or kettle gets charged, the current should flow to the ground with high enough amperage to trip the breaker immediately..
Go brew something!!! :)