1. Orochimaru got all his strength by himself.
2. Kabuto is a thief... -.-
3. Sasuke didn't get Amaterasu from Itachi... -.- Sasuke could have gotten the MS many years before that, but he choose not too. He could also have gotten teh MS through training, but because of Obito's mouth that never happened. But as of now it has only been said that the ways to awaken the MS is to either kill your best friend, experience something really dramatic ( Like Obito, Rin's death ) or by training until you are 100000 years old... If you really mean that anyone gave Sasuke the MS then that person is Obito, not Itachi. Also Itachi died to Sasuke, even thought Itachi wanted to die by Sasukes hand. He still died to Sasuke hand... Also Itachi would have died of sickness long before Sasuke's fight with Danzo if Itachi was still alive at the point. THen he could simply have taken his eyes then, like he actually did... -.- The only reason Sasuke needed the Curse Seal to was to kill Oro with it again.. xD So simple said, Oro borrows Sasuke something for 3 years and Sasuke gives it back to him through Itachi... xD