Which, IMO, it would be better to let the engine sort the objects by class and determine what will be passed to the render engine as shadow caster/receiver. Beth did that. They just restricted the list to rigged objects. Originally they were using cubemaps for shadows (ref: E3 demo) and even clutter was casting shadows. But performance was an issue so they axed the whole system before release.
You are totally correct about this; the things I know are that:
1. The list of all object classes is still in the game code.
2. The selection parameters are still present in the game code.
3. The Oblivion code on shadow casting can't be looked into.
4. The Fallout code on shadow casting can be looked into.
5. The code on shadow casting for Oblivion and Fallout are the same.
The only problem is I can't change the things I found to make it work jet.