Kerrick's point is that your magical power was partly limited by the fact you had only so many slots to take up. If you wanted to free up slots, it either cost you 50% more (add it to another slot) or 100% more (slotless).
With the new system, while the big 6 aren't the only items a player is likely to get, they are easier to get because he doesn't have to worry about slots anymore (hmm...should I get gauntlets of str +2 or gloves of dex +2....oh, I'll just get both and put them in the same slot).
But on the same token, the idea of the MIC is to provide neat alternatives to the big 6, so that while players are still going to get resistance bonuses and stat bonuses, etc, they may wait on them awhile to get some of these new cool items.
My main concern is that some of the new items are so cheap, many players will have no problem crafting slotless versions of them or add them to other items (assuming the DM allows it). I think some of the balance of these items is the slots they take up, when you remove that they may become too powerful for their cost.
I'll give an example, the boots of ultimate athletism. Lets you take 10 on some physical skills, and 1/day you can take 20. As is, its fine, takes up a boot slot, some people will love these, some will want boots of speed or boots of flying, etc. But if I can combine that with another kind of boot I just gained a high level rogue class ability for dirt cheap. Its something to be wary of.