I got guildwars just over a month ago, loving it

I've noticed while browsing the weapon screenshots thread, that all weapons of one type do the same ammount of damage(all necro staves do 11-22, dervish scythes do like 9-41, all assassin 7-17), ofcourse excluding earlier reqs.
What is the point of having different weapons if they all do the same ammount of damage?
Thanks

-Dudman