Kyubi's Sealed Chakra

Your two options may very well be right but we must also keep in account the fact that he only sealed his yin/yang (I never know which one) part which gave naruto an abudance of a certain one of the two. One has something to do with the uchiha and it's like mental power while the other one is more physical. This gave Naruto trouble with the bunshin technique but exceptional progress with the kage bunshin technique. It could've been used as a plot device to further make clear the opposite relation in sasuke/naruto or it's simply kyuubi hype because even a suicide hokage seal technique can only contain half of its being.