The more powerful the item is, the higher the chance that it will be picked up, generally. Hence, you might not be able to pick too many rings of tamed lightning, but items of unique quality will be picked up more than likely.
Ahh, okay. Thanks for the info, guys. I was giddy when I saw it and after the battle I was like "Okay, now where is it?! Where's my precious!?"
BTW, this is the demo Version so I don't have any documentation handy for reference but I just dl'ed the manual for Dom I. I'm assuming most of the info hasn't changed much...