I think superintellegence implies superior mastery over the forces of nature. It implies the capabilities of a superengineer, a superresearcher, etc. And so, it should imply a drastic progress in biomedical science and medical practice among other things. (Of course, people can define the same notion differently, but I am quite certain that Nick Bostrom means it this way.)

Pragmatically speaking, why on Earth would I need an "owner", if that "owner" can't reverse my aging, fix my future cancers, and postpone my mortality indefinitely? What would such an "owner" be able to give me, which I don't already have? Nothing seems to come to mind...