First off, you're over thinking everything including my explanations!
Obviously we still need multiple lootdrop tables, that's why I didn't touch that. What I mean simply is we now have ways to reduce all of our tables down to 1 if we so choose. The old way, we essentially were forced into using multiple tables.
Okay, completely forget about the old system... Probability never existed, in fact EQEmu never has had a loot system before today. As a human, when you flip a coin what is the chance it'll land on heads? 50%. Now do you think well, it becomes 25% because there is a 50% chance I won't even flip the coin? No. You will always assume whatever prerequisite is already met before figuring out chance. That's what I've done. That table is always going to roll true, you're always going to flip that coin. Now what do you want the actual chance of an item dropping to be? We only multiplied chance by probability to convert to the new system. From here on out, forget about doing that in your head. How often do you want the item to drop, figure that out and put it in your DB!