Nail said:
So a weapon would be a slotted magic item if its powers were only effective when drawn and held. If you think about it, wands and staves also fall into this category; they must be held to be effective. Thus their lower cost. They are effectively slotted items.
The point of slotted items isn't that they have to be activated (although many of them are "always on"). The point is that having an item in a slot prevents other items with different powers from occupying that slot. Thus you can't have both an amulet of health and an amulet of natural armour at the same time, unless you put the two enchantments on the one amulet, and pay extra.
A sword with a strength enchantment isn't slotted, because it doesn't prevent other enchantments being put on the sword. If you do the arithmetic, it all works out in the end.