On Merry not needing an enchanted blade, someone told me once that Merry, and for the same reason Eowyn, was able to kill the Nazgul
because he wasn't a man. He, or she (I can't remember who I was talking to), thought that when the Witchking said no man can kill me, that he meant that only women or other races could.
Just thought I would add another explaination. Maybe that's what PJ thought
