The bottom line that some people here seem miss is this:
A wizard with some basic raid (+2 focus, +2 tome, tod rings for +3 exceptional stat) loot and a skilled player will be able to contribute much more than most epicly geared melees can in almost any given epic quest. The same goes for divines.
With a dc of 40 for necro and 37-38 conju and enchantment you can lay down cc and still get most of the kills almost everywhere, the melees are left with the few that do make the saves against your instakills. For a fresh wizard, getting dc to over 40 in one school is not hard at all after some raiding. As you get more gear the gap will only widen, to the point that taking another melee instead of another equally geared and skilled arcane or divine caster is a wasted spot in the party.
This is why there is even less balance than there was before, if you want optimal, you go full arcane and divine and don't take any melees (except maybe an assassin III rogue), how long will it take until we start seeing parties that are looking for just one melee for tanking if there doesn't happen to be a wf sorc or a favored soul with some hp around?
Or maybe that won't happen because people are too ignorant to know how to play their class to it's full ability and won't learn how to either. Not that I really care, I still enjoy playing melees and I'm doing TR's for my fighter atm, so whatever