That text appears on everything from bone chips and deathfist belt turn ins to epic turn ins. You also see the text when other players have completed quests that only have one piece to turn in. So i really doubt the reasoning was to make quests easily MQable.
They likely did make a decision not to patch them out or maybe it was just a limitation of the game at the time and couldn't be done. But I fail to see the point of making any quest items no drop if the intention was to allow players to essentially sell or trade them.
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