I think he means "give them items so uber it is like they are spellcasters" which, of course, is blah, at least to me.
I still think the best thing to do is have longer casting times allowing for interruption by other than readied actions, and nerf concentration.
First, to the OP...balance is an illusion. Balance suggests a empircal comparison which is nigh impossible in a PnP RPG. The best you can talk about is "fairness" and that is subjective. D&D 1e was never meant to be "balanced." The DM was supposed to make balance irrelevant. As D&D has evolved, it has moved towards this concept of balance...which is ultimately going to be an albatross arounnd its neck. You can't balance things that do not all conform to some unit of measurement. What exactly would that be in a PnP game? Damage? Only about 1/3 of my campaigns require actual killing to earn experience.
So what happens is D&D is forced to a balance powers and feats and actions so that no choice is any more or less "powerful" than any other. You see this with MMORPG's. Take a game like City of Heroes. All 1st tier attacks are balanced along the same scale: Recharge, Damage, Endurance. This means that power can
feel different, but all be equally effective. In other words, the mathmatical DPS is nearly identical. You can't do this with D&D...without fundamental changes: enter 4e.
However, I do agree that when class ability/power is too out of whack, it can make it difficult for characters to operate in the same campaign. That having been said, I think kittyitch's idea is a very very good one. By forcing a caster to take 4 rounds to cast Fireball, you basically require that caster to rely on the burly types to protect her. It also means that in a 1v1 fight, a caster is not going to be able to pull out the heavy artillary and simply blast the fighter into oblivion. Similarly, you allow defensive spells and utility spells a shorter time so that survival is easy, victory is not.
I think this is really the best way and the least game breaking way to mitigate the imbalance. Too bad WotC didn't adopt it, play test it, and give us a strong guidelines for setting those casting times.