Certainly I'd say there are a myriad of ways features can be implemented. I think we are both on the same page here to illustrate that it is not a system resource limitation, but likely a function of available dev time and project resources.
Anyway to continue this discussion... I don't see corpse counts as a large issue on a PC platform but console resources are at a premium and any title that wants to support this feature would likely be devoting extra dev time to give a bonus to PC players.
I'd say exclusion from the tree the best way to treat corpses while maintaining available resources. With HW accelerated physics more items can be populated into the tree with less impact, but when using SW its best to keep the extra items static. Of course you can go to the extreme as you mentioned and maintain proper IK on all models and ragdoll. But that just more eye candy to encourage players to perform lewd hot beverage based acts with.
As for collision between the corpses-- additional exclusion of items from the AABB tree would required to keep body physics separate from gameplay items. In my previous statement I noted certain items required for quests may be obscured by corpses; while the corpses themselves may not collide with the player. That something that needs to tackled separately. If corpses are excluded you can make them semi-transparent allow interaction between players and objects below them.
Exposing user selectable collision types is likely unproductive, and may result in unforeseen exploits and support issue. A setting for limits, both time and count, could be exposed without much issue though.
