You are right. The NSX is one of very few cars that a rear BBK is worth the $$. Most front engine cars at threshold braking have very little weight on the rear tires, thus rear brakes will easily lock, and do little to actually slow the car. i.e. with my integra bought new in 1998, I went through about 20 sets of front pads with a BBK due to track use, and my wear bars on the original OEM rear pads just started to squeak in 2003 when I sold the car.
The NSX has extra weight in the rear such as the motor, tranny, and differential, so under heavy braking, some of this weight is transfered to the front, but much remains over the rear axle.
NSX's with front only BBK's generally lock-up, or kick in the ABS real easy, so good track tires are almost a must on the track with a front only setup. Hope this helps.