Ship cats are different from other cats.  They are just as intelligent and just as self-centered as other uplifted cats, but they seem to have a deeper need to join our world.  They enjoy being with us, enjoy working with us, and love to spend months or years in space with us.  They are still indefinably cat, with alien thought processes that most of us don’t understand, but they are the original goal the gengineers sought.  They are the primary link between our races.