Board Thread:Naruto Discussions/@comment-25294339-20141101162145/@comment-4685024-20141102044041

I say the most logical explanation for Obito reviving Madara has is that Obito needed to fully rebuild Madara's body and reattach his soul to it, which is much more complicated and taxing than just summoning a soul to return to it's body. Madara's soul was also already there, so the King of Hell would not need to used.