The slaves developed this clever skill in order to use the forces around them to be able to overpower the noble class, thus becoming the complex creatures that we have become, always looking at things in layers of existence. It is how we understand the world to work because it is the way that we ourselves have made the world. An Ubermensch does not need to look to the forces around itself, because it itself is a force. That would be like expecting the wind to look to the other elements before acting and attempting to figure out a way to use them. It just doesnt happen. The primal force that drives the very wind would be the same force that I believe we would find within the Ubermensch. These creatures are the perfection of humanity and thus they would fit perfectly within the perfection of nature without the need of extra man-made skills such as intelligence, rather they would just BE, and in that act of being their wills would be as unstoppable as the forces of nature that develop our world on a regular basis, nearly God like, but not in the Judea Christian sense of the word.
I dunno, Just an idea of why intelligence isn't included, what do you guys think?