Well if I recall correctly, somewhere Tolkien states that the nazgul were never good fighters, or at least that was not their purpose. Their purpose was to create fear in the opponent and allow the evil minions to kill them. And I know for sure that Sauron never sent them out to fight as champions, they always were doing special tasks for him or serving as the overal commanders of the battles, fortresses, war effort, etc.
Maybe someone who remembers more can help me out on this... it's been about a school year since I've read the books
but I'm going to fix that this month.
Edit: Aragorn beating them has nothing to do with it. Again I'm pretty sure Tolkien states somewhere that Aragorn owned them due to his surprise attack, the fire he had, and the fact that he was the 'last' descendant of numenor (something to do with how the nazgul could feel or tell somehow that he was no ordinary man... I think...).
Edited by GothmogtheOrc, 11 May 2008 - 02:01 AM.