There are differences:
Special move is unique plus (I can't find this post) a wizard gets more mana from intelligence, for example and there are damage differences. Search the forums and you'll find this post, it's by Raze.
I must agree that these differences where just not enough ... but don't be sad since there won't be any classes at al in <img src="/ubbthreads/images/graemlins/riftrunner.gif" alt="" />
