Blizzard Quote [source]

That’s one of the reasons we added the Monster Power system: it allows players to further tune how challenging enemies are in each difficulty setting, regardless of level. Also when Travis Day spoke about allowing Legendary items to scale up in our recent Developer Journal: Itemization Update, that means they will be able to drop at lower levels too. We’ll be looking not only at letting low-level Legendaries drop at higher levels, but we’ll also be allowing higher level Legendaries to drop at lower levels. In addition, the targeted drops we mentioned in the Itemization Update are intended to improve the level up game as well.

Below are some specific examples we’re considering which we feel will benefit all players, regardless of level:

• One idea that we have discussed is “targeted Legendaries,” where named NPCs have an increased chance of dropping specific legendary items. For example, The Butcher could have an increased chance of dropping The Butcher's Carver.
• Another idea is that we introduce a system that will help alleviate some of the bad randomness players encounter by ensuring that at least some of the Rare and Legendary items you find will be something good for your class.
• We've also discussed allowing bosses the first time you kill them in each difficulty to have a guaranteed chance to drop a Legendary.