It would make sense to me to be able to fly a single channel CAT 2 approach with a manual landing if for some technical reason, A/P U/S etc a dual channel approach could not be flown. Single Channel approaches do not produce the nose up trim of the dual approaches on the final stage of the approach,so do alleviate that problem.
The J-41 was certified for CAT 2 approaches and only had one autopilot..what is the difference really? Well apart from size, speed and noise!!!!
I should imagine it is a company thing, it would take extra time in the sim ( they can be a tad tricky!) .And I can understand that during the low vis ops time in the box, they would prefer us practising CAT 3 approaches.
If i remember correctly, and I will have a look in the books tomorrow, the early generation 73s are fail passive and the NGs are fail operational but for commonality companys treat them as the same.