I'm one of the posters you researched. When I asked these LBS mechanics why they only snug them down, most responded that in their experience, that's all it needs. A few also suggested to only snug the driveside as well in order to ease removal. None were able to give me any theory on the matter when I probed, but I decided to give some credence to their advice, assuming they have all likely done hundreds of these in their careers.
One thought I have is that because the spindle and cups are one piece, and the the bearings only apply pressure to the inside of the cartridge body, there is less of a need to secure the cups. On an adjustable cup bearing assembly, the bearing balls are constantly working on the cups independent of the spindle. There's no body to hold it together.