I'm not sure exactly how they have it implemented. If we knew that there were only a few possibilities for drop rates, it might make sense to try and pin those down. Certainly it seems like when a monster drops a ton of different things (e.g. research components), many of them have the same chance to drop, but it also seems like that chance can be different between different mobs. Anyway, I have no idea how it works, I'm just trying to get some good statistical results from observation.
I've now updated all my entries in the wiki with confidence intervals (these are mostly for low-level mobs and I'm still in the process of getting more data, and will be for a long time). Here is an example of a monster with 415 kills:
http://wiki.project1999.org/A_decaying_dwarf_skeleton