Well, I've been giving it thought. People(Including myself), when Obito was revealed to be Tobi, were like...."WTF, HOW DID HE SURVIVE!?!"....My theory is that he didn't. Uchiha Madara would have had the Rinnegan at such a point....Which is where the next part of my theory comes into motion.
Assuming that Obito did die, Madara would have needed to use Rinne Tensei to revive him. But, this is what it all hinges on, but here's my thoughts on it. From what I can see(without reading the actual jutsu description in the databook) Rinne Tensei simply puts the soul back into the body. But, with this in mind, it's easily feasible that Madara would(or could, depending) put a different soul into Obito's body.
On a completely separate note, this has been bugging me for a week or so now. Taka joined the Akatsuki to hunt Killer Bee, but before they had been given their assignment, Suigetsu tried to start a fight with Kisame. Tobi blocked Zabuza's sword with his hand. Does this mean that Tobi can change the makeup of his own body(or rather, swap it out with anything that he has in his other dimension, AKA the massive shuriken and the chakra rods he was tossing all over the place recently?)