Outer Limits 4x4 Board

OK. looking at a RB30 shaft front & TB42 shaft front. They are both the same length but the 3.0l has a smaller flange but a larger diameter shaft. Also the flange has a lip that fits into the rebate on the dif flange. The 4.2 has larger flanges and smaller diameter shaft and the shaft flange is rebated which is completly opposite to the 3.0ltr. WHAT THE?

Can anyone tell me why this is so because it makes no sense to me!

Rear shafts have the same set up as well

Thanks