Considering there is no proof at all that Sasuke has been given the MS by Itachi, only the Amaterasu, I'm lead to believe that Sasuke's power is a partial MS.
Amaterasu comes from within the left eye. Tsukuyomi comes from within the right eye. And Susanoo is expelled from the nose. (based on shinto religion) My theory is that Itachi passed the powers of his left eye over to Sasuke to protect him. I also think that it's possible that Itachi might have given Naruto a piece of his Tsukuyomi's power (what part is unknown) to help him win against Sasuke.
Itachi wanted Sasuke to be strong enough to survive, I'm sure he knew that if Sasuke didn't have at least Amaterasu, Madara would have no use for him and would probably kill him. He also knew Madara's plan to take revenge against the village. Hearing that Naruto had no intentions of killing Sasuke would make him a prime candidate to recieve a power equal to that of Amaterasu, which along with his Kyuubi side he would be more than strong enough to handle anyone. If you really think about it, even if naruto learns all of techniques in the key and learns hermit mode AND gets over his hesitation of using the Kyuubi's chakra, he probably wouldn't stand much of a chance against Sasuke/Madara together. Lets face it, Pein killed J-man and he had two of three of those things and Pein is subserviant to Madara. What's more is, I don't think we will find out what the "Power" that Itachi put into naruto is until the end of the next 100 rollover.