That's a very good technical description of the parts involved - but I think everyone on the thread ?probably? already understands the parts involved. I know I do.
When I look at this drivetrain as an entire system - it really does appear to me to be a RWD system, with front assist. And everything you just described lends credibility to that observation. A true 4 wheel drive vehicle (trucks, jeeps, etc) would never dream of using a center differential. The F&R drivelines are directly connected with no clutch in between so that whichever end of the vehicle has grip can use 100% of the engine's torque. And as such, the Front and Rear differentials and axles are generally similar in overall strength, usually a bit more in the rear than the front, but close.
Looking at the GTR, however, not only does it have a center diff that "protects" the front end by limiting the amount of torque sent there, but the GTR also has that FWD clutch before the fron output shaft, which further limits the amount of toqrque that can be delivered to the front end. All this adds up to my assumption/observation/whatever you want to call it/ that they are not expecting the front tires to ever do more than 50% of the work in moving the car. And therefore, they felt they could "get away" with using smaller and lighter components in the front half of the drivetrain, due to the "protection" that the center diff and FWD clutches provide.
That's just how i see it, looking at things from an overall strength perspective... The car is great, but the front end is not built to be as strong as other AWD cars that I've owned (Audi)
EDIT: RPM - yes that's correct. Lots of manufacturers are now using the brakes to act like a LSD. The first one I recall off-hand was land rover in the late 90's. The one's I've driven work OK, but not that great. In the off-road world, you really need lockers or spools. In the road racing world, a LSD in the rear is a must have, but in the front, I'm not so sure - I think it would mess with the steering quite a bit (think torquesteer in FWD cars) during corner exit, and possibly produce throttle understeer. On the drag strip, however, I think it would help if you are making enough power to spin the fronts during launch - I dunno, I'm not much of a drag racer...