I think what you're referring to is that mats can drop from almost everything, which is different from mats dropping from enemies on the drop table. I believe the way it works is all enemies have a drop-anything rate (DAR), and when that is passed, the enemy will either drop it's rare (from the drop table) or something from a list of items, including mats, orange and blue boxes, pd, meseta, etc. If DAR isn't passed, the enemy drops nothing.
I'm not 100% sure if this list of non-rare drops changes from section IDs, but I wouldn't be too surprised. I remember reading a guide on pso-world that mentioned certain IDs finding certain non-rare things more often, like Skyly finding orange box swords and power mats more often than Pinkal, for example.
Hope this answers your question, and if not, someone with more knowledge about the game can answer :v