It is a general video game thread, as long as we dont start talking about hunting it is ok.
I think it is the entire light/dark duality. There is one missing, but fine, I see your logic, kind of, if it wasnt for the fact that it isnt called Light, or Good, it is called Fairy. Ghosts being weak to Fairies? Could accept that.
Steel makes more sense though. In about every kind of mythology that has fairies they are weak to cold iron. Their weakness being Steel makes perfect sense. But yes, Poison did need it.
Ok I see your point. Still, Rock could be a weakness, that would make sense, considering Electricity doesnt work on Rock.