Possession or omission with one exception - and that's all

Pointless, I know, but I'm going to get this off my chest...

How is it that so many people cannot get the use of the apostrophe correct? The rules for its use are simple and have only one exception (example of which can be found in this sentence).

Possession - "Joan's painting (noun)", "England's captain"
Omission - "That's all folks", "Don't get me started", "Joan's painting (verb)"
Exception - "It's a long way to Tipperary", "The rules for its use"

And that's all - it's not for awkward plurals like abbreviations (DVDs not DVD's) or nouns ending in vowels (casinos not casino's)

IT IS SO SIMPLE!

I feel better for that...