From my very limited knowledge on this subject I do believe that each individual component sould have been made with a different impedance to be able to come up with an 8ohm cab.
A guitar speaker can be made in 4ohm, 8ohm, an even 16ohm with what I believe is no difference in performance when each is driven by its appropriate power source.
What not the answer you wanted?
Rick
"A fear of weapons is a sign of retarded sexual and emotional maturity." Sigmund Freud