Really late to the conversation , but I have a few generic comments (probably not too related anymore, so stop reading unless you have plenty of time to waste) . . .
I think on the consumer side the real issue is laziness, not intelligence. I'm conceited enough to think I can easily do the math (I was a chemistry major) but getting the numbers (residual levels) is not easy (and I'm lazy). I've never seen a water report in my area and I couldn't find one online. Given I live in a small town, I'm guessing I'd spend a lot of time calling around just trying to get in touch with someone who could answer my questions (on water residuals).
Of course I could test my water, but I'd need to do it many times to truly get useful data (although testing just prior to a water change would probably be adequate).
IMO relating math ability with intelligence probably indicates our own personal biases. I think it's better to think of math ability like (foreign) language ability- the more exposure you have and the more you've studied it the better you are likely to be at a given language (or subject like math).
Now the humbling thing is to admit that even though I have 2 degrees in chemistry, I never thought much about the chemistry in our aquariums. I just "cook-book" it, following the directions on the bottles. Not thinking about it, I hadn't considered the ramifications on O2 levels due to excessive dosing of Prime.
I'm guessing most hobbyists, including myself, have usually assumed that more Prime is the safer default than too little. Since I mix my water, salt, and Prime in a separate container, and allow it to mix for a while, hopefully my O2 depleted water (due to excessive Prime) would have time to come to a new equilibrium, but since I have no real guesstimate on the kinetics of those reactions, I'm really just hoping everything will be fine.
Give me the data and I could calculate it, but again, I'm just too lazy to put the time and effort into getting the data.
If you actually read all of this post, you're either really dedicated to this topic or really bored since I've just been typing randomly with nothing pertinent to add to the conversation (except the clarification that poor math ability does not mean low intelligence). Sorry to wast your time!
[The math geek in me finds this topic interesting since I enjoy algebra.]