I think that you can find the main reason of this success in the words Leto used in his acceptance speech. "This is for the 36 million people who have lost the battle to AIDS and to those of you out there who have ever felt injustice because of who you are or who you love, tonight I stand here in front of the world for you".
By the way, we are also proud to mention the victory for the Best Foreign Language Movie of the Italian ‘The Great Beauty', about which we already talked too, after its success at the Golden Globes together with ‘Dallas Buyers Club'.
Happy Oscars guys, enjoy, you deserve it!
Source: DAA website