Relique du Madde
Adventurer
Actually, I don't think thats entirely true. I think I remember an episode from Highlander where Duncan lost his hand and it did regenerate.
That type of regeneration is what I like to call a plot device power. That is, it only happened once because the writers thought "it be cool if Duncan got his hand cut off" only to realize that "Duncan's actor isn't ambidextrous and it would be impossible to pull off Duncan having his right hand cut off for more then one episode."