Your right, but look at the picture I posted of the size of the mags next to each other. The 232 is vastly smaller than the double stack mag, small enough where even with the difference of polymer mag well vs screw in grips I think the Sig grip should/could be smaller.
SIGs have always been a bit thicker. The standard grips of years passed compared to the E2 style of grips they use now are much thicker. Why? They didn't need to be. Maybe SIG thinks there is something to be gained in trying to appeal to those with larger hands that want a larger grip?
Anyway, it won't change the current situation. Could always call SIG and voice your opinions to them too.