Sorry if there is an answer for this kind of question somewhere. I can't find it anywhere.
Take a look at obvious toaster example: If you live in Europe and have non-polarized plug and a toaster (a bad one without double-pole turn off) - you have a 50% chance of touching the hot wire (via the heating elements or even bread if you're unlucky) if you plug it in the wrong way, so that the off switch turns off just the neutral wire. You will be shocked if you somehow connect your body to ground (through another device for example).
I understand that these conditions are not very likely to happen, but why do many countries still not even think about doing away with non-polarized sockets and adopt polarized? I'm sure even in Europe the light-bulb sockets are wired to be neutral-shell polarized, so why not wall sockets?
Sure it is not a cheap thing to do, but 10 years later it will be even more expensive since more stuff will be produced without a polarized plug.