The issue keeps coming up in clan chat, so I figure it’s worth quoting another Blue on the issue, since the rules changed again earlier this week with the 2.0.3 patch.
This has, indeed, been changed, but it also depends on what level you are.
Players who are 1-59 will find that the first time they kill an end Act boss (Butcher, Belial, Azmodan, or Diablo), they will receive a Legendary. Players who are level 60 will receive a Legendary upon defeating Diablo. If you have already defeated Diablo and are not receiving a Legendary, using the “Reset Quests” option will allow you receive this bonus again! However, be aware that you are required to complete every main story quest in the campaign in order to use this option. This also works for resetting the first-time kills from 1-59.
Hope that clears things up!
The guaranteed legendary from Leoric was (apparently) always a bug. So when the last patch fixed his guaranteed drop after a Reset Quests, it also took away that first guaranteed orange for low level characters. Maybe Blizzard should have left it on Leoric, with a low level requirement? Say below 15 your first Leoric is a guaranteed shiny? Oh well, you’ll find plenty of others as you level, and anything you find at lvl 15 is outgrown by 20 or 25 anyway.