I agree, I saw the reason for the switch from Morrowinds "Kill everyone but certain NPC's will bring a pop up about breaking the game" to Oblvions "Essential Immortal NPC" to prevent people from accidentally killing an NPC either without noticing or accidentally. But quest items should NOT be undroppable. At the very least they should be weightless.
If Beth wishes to prevent people from losing the item in some random dungeon then simply make it so quest items can ONLY be dropped in a house that you own or a chest within.