No, they haven't; however it's not that hard to get good loot sometimes. All you have to have is have the quest already active when you face the boss, this increases the chance of getting a rare item by a fair amount. In some cases, (the only one I actually know of is The Warrior) there's actually a 100% chance of getting a rare item from him, as long as the quest to kill the warrior is active.
Otherwise, it is still very difficult to get rare items, that's why they're rare!
Hope I helped!