Why are there so many different explanations for forming plurals?
I'm trying to learn how to form plurals and found the Duolingo notes & tips section a bit confusing so had a look at a few places but they all seem to have different explanations.
For example: http://masterrussian.com/nounsandcases/gender_and_number.htm and http://www.russianlessons.net/lessons/lesson11_main.php both seem to tackle it slightly differently.
I'm sure the end result is the same but it seems a bit strange there isn't a single set of rules that everyone seems to follow.
In other languages similar to Russian, such as Latin or Ancient Greek, you'll find the same thing--various ways of explaining the very same language phenomena. As there's no central authority, different teachers/grammarians like to explains things in their own way, I guess.
We don't have a simple rule like "Just add an S in the end, and you're done". Instead, we just know what the plural for a given word is. So, if a course is built by native speakers, they probably think something like: To form the plural form, you have to... oh wait... what's the rule? Okay, яблоко - яблоки... облако - облака... дом - дома... кот - коты... oh my, they are different! And then they have to sit and find some common patterns :-) So it comes as no surprise that different authors end up with different ways of teaching the same thing.