There are no robes / staves / wands in D2:ED. Robes are relatively easy to do in a 2D game; for a 3D game if they don't move like cloth (which is fairly resource intensive) reviewers would probably critique the game harsher than simply not having robes, if they noticed that at all. Any resources devoted to adding robes would also have meant something else couldn't get done.
For the lack of staves and wands (or two handed hammers, etc) I don't know if that was a deliberate decision to simplify combat a bit, or if there just wasn't enough time before release to get them in. Any different weapon type that would require a different animation would make collision detection more complicated and perhaps slow down the testing process (though I have no idea if that was actually an issue, or not). It could also make balancing more difficult, though if they were going to add mage class weapons, they could have dropped the normal weapons doing magical damage (bonuses on weapons could still add magical damage to the conventional melee/ranged damage).
