Jeff Kaplan has said some interesting things at this year's GDC (expect a full account from us soon). One of them concerned a new technology that debuted in Wrath of the Lich King which I, for one, had not heard of before: progressive drop rates for quest items.
Pre-Wrath, if you're on a collection quest, whatever you're trying to collect will drop at a constant rate (35% was apparently the standard). Overall, this averages to a predictable amount of kills per quest. But probability being the way it is, it was altogether possible to have terrible luck and have to kill 100 foozles to get your four gizmos, or to have great luck and get your gizmos in only four kills. It was the bad streaks that the devs were particularly concerned about, as those are very memorable and never fun.
In Wrath, according to Kaplan, drop rates for quest items are progressive - the more foozles you kill, the higher chance each one has to drop a gizmo. The standard quest item drop rate has been raised to 45%, and each kill you make raises that drop rate by some amount. Kaplan said that it can eventually reach 100%, at which point every kill would drop your item. This puts a hard cap on just how frustrating a collection quest can be. Seems like a smart idea to me. I hadn't really noticed Wrath collection quests being easier, but then, I wouldn't - I simply wouldn't have bad-luck streaks, the absence of which might not be easy to notice.