DUH? i mean it was CLEARLY stated in the manga. Kabuto even said him and orochimaru had this theory going on for years and when madara finally used his rinnegan kabuto/orochimaru's theory was proved to be true...
sucks we didn't see ems being used that much
madara didn't even have to steal eyes from his brother all he had to do was awake rinnegan and still be the same i guess =/
We don't really know for sure though. Nagato had the rinnegan but he never had used sharingan powers (like most people are saying that the rinnegan can use powers like the sharingan.)