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).
That's exactly what I meant, thank you.
I think body-slots are not a great way to control magic item use and abuse. It's a relic of the old editions. Now we have bonus types that don't stack and THAT's the real way magic items are managed.
"Body slots" weren't formally introduced until the advent of d20. Before that, there were just guidelines as to what you could wear and where, and how many (one ring/hand, e.g.). I agree, though, that using ability affinities with the slots makes a bit more sense.
Imho, with the advent of the MIC the DMG guidelines for pricing magic items have become obsolete.
The MIC made them obsolete because the designers pretty much ignored them and made their own. Case in point: adding multiple abilities to an item is now 1.5 times the lower ability cost, instead of 2 times the higher one. This rule in particular is the largest part of my problem with the stacking abilities system - a smart player who wants an ability-boosting item will get himself something cheap, like boots of levitation, and add in a Dex bonus at cost, instead of the price of the entire item x1.5 (or the lower price x1.5, depending on which system you use).
Personally, I like the idea of a character with one or two reallly powerful items than one with a hundred different items all over (and orbiting) his body.
But... this book is encouraging the latter, by making everything cheaper, and making combining abilities cheaper also. Which is my second major gripe with the book - players were limited in the number of items they could have by the number of slots they had and, to a lesser degree, by their wealth, if they're made from scratch). You're still limited by slots now, but with the cheaper costs for combining things, you free up slots for other things - more magic items.
By the MIC, adding +2 dexterity to a pair of Gloves of Manual Prowess now costs just 4000gp instead of 4000*1.5 = 6000. But what if I already have gloves of dex and want to add the manual prowess feature (base cost 3000)? Would that cost 3000 or 4500gp?
4,500 gp. Ability bonuses added to an item don't incur the x1.5 cost, but everything else does.