I'm guessing people have been playing the same character since release? In my most recent character all the items you mentioned get removed upon quest completion and I've learned not grab quest items unless I'm on the quest.
Problem is, there are quest items that are not obviously quest items until after you pick them up. Like the books for the Orc in Winterhold. I shouldn't have to log online to see if a book I found is actually a quest item so I don't pick it up.

