It's total bs marketing spin, *any* car will have 50/50 distribution at some amount of accel (or decel for rear-biased cars).
If the GT-R's static distribution is more forward-biased, it's not as big a deal because all the wheels contribute to acceleration driving out of corners.
On the Z, it's a bigger deal. And again, even 50/50 static is not "perfect", you want a more rearward static bias for a rwd car with any kind of decent power/weight. 54/46 is a piss-poor static weight distribution for what is *supposed* to be a sports car. Fricking Mustangs and Camaros and the like have that kind of weight distribution.
Oh, and the GT-R does NOT pull 2g of lateral grip, that's off by about a factor of 2!