Have changed many diffs in my time but all have required thrusts/preloads, backlash and pinion to crown wheel measurements/adjustments et al to be made. Usually meaning the damn thing has to go in and out at least three times! This looks to be pretty simple in comparison . . . except for the weight issue. I do have various jacks to help on that score though.
Thats a function of the design. Theres essentially two common ways to build a diff.
On some, (Ford Atlas or Landrover Salisbury for instance) the cast part the holds the pinion and centre bearings is part of the axle case. On those, you have a removable rear cover on the axle case, and then need to load a bare diff into the axle case, and thus need to setup all the preloads and pinion engagement etc.
On others, like the P38 (and other Landrover Axles), or the Ford English or 9", the cast housing holding all the bearings is a seperate piece which bolts into the front of the axle case. With those, you can thus have the cast "pumpkin" all setup ready to go so it just needs to be installed into the case.
I guess you've just been unlucky to have always had the former style.
Ofcourse, to fit the actual diff into the cast part still requires the same work. The advantage being you can easily ship the bolt-in cast housing and thus have someone else do the work for you, rather than having to ship the entire axle.