The OP is basically asking "why are there fins on a cadillac?"
I almost posted the same thing!
I can see how that lower offset bulge might help with the ergos & balance. (Though I just A/Bd the P & J and must say the difference is not dramatic.)
To be honest, even if the offset contours made the thing almost unplayable, I'd probably still lust after it because I personally think the J-bass is freakin' gorgeous.



