I think it has to do with the fact that the rudder it attached to the keel. No part of the rudder is forward of the rudder shaft.
When it isn't, like a fin-keel boat with spade rudder, I think that there isn't enough lateral surface area back aft to provide lateral stability, so they have to add area back there. They might add this area forward of the rudder shaft to balance the helm somewhat.
Just a guess.
I can say from experience that the Ariel tracks like its on rails, but my 35' C&C could probably turn a 180 *inside* the same turn by the Ariel. (it would be close)
-km
aka, "sell out"
S/V Beyond the Sea
C&C 35 mkIII