I would tend to agree. The effective gravitational influence of a star would be relative to its mass. We can pretty easily determine the (rough) mass of a star,

I would tend to agree. The effective gravitational influence of a star would be relative to its mass. We can pretty easily determine the (rough) mass of a star, and ours appears(?) to be somewhere in the middle, so it stands to reason that 8-ish decently sized planets is not an unreasonable number.