Downvote if you want. Being smart in programming or business stuff doesn't mean you understand linguistics. Organic language does not adhere to logical rules.

Many people (who don't actually study language or the evolution thereof) jump to a Prescriptivist viewpoint at first. Dictionaries follow actual English usage, not the other way around (Descriptivist).

I can't fault you; in order to teach English a prescriptivist mindset naturally has to be applied. So we teach Standard English's rules.

However, go compare various English style guides and tell me if they are the same.

Dwarves & Octopi are correct, because that's what people use. If octopedes was used instead, it would be correct and it wouldn't have a red squiggly line.