Why does engine type change gear oil recommendation?

[04'Sport4WD]

According to my owners manual, if you have the v-6, it recommends 75w-90 in both front and rear diffs. If you have the v-8, it recommends 75w-90 in the front and straight SAE90 in the rear. It seems like every thread I've read stated people were just using 75/90 in both. Any thoughts on this?

 

[coldbivy]

I don't think it has much to do with the engine.

My 05 manual recommends 80w-90 or 90 on the rear of the V6 and 75w-90 in the front.

For the V8, it recomends 80w-90 or 90 in both front and rear.

I assume this is because the front is full time in the V8.

I also have a feeling that the early versions of the manual have lots of errors in them.

Has anyone actually had a diff fail on them? I haven't and none of my friends have either, so I'd guess it is extremely rare. As long as you keep som gear oil in there, I don't think you'll have a problem.