as far as i know (and makes sense too) abs is not really to reduce stopping distance but more to allow steering while its doing its thing.
when u lock up the wheels u have very little chance of steering but if u have abs it is a lot easier to steer the car while the brakes are pulsing.
in your case u probably did not have it from factory, and personally i prefer r33 gts-ts, 300zxs, and 200sx's without abs as they all have much less feel than the same model without abs. r33gtrs in my experience still have good brake feel, they use different calipers etc which would explain the difference if not the ABS unit/software itself being much different. anothing thing that annoys me on the other nissans is that the abs kicks in too early, this is once again different on gtr's.