This “Brexit” coin has a missing comma, depending on your opinions on the Oxford comma. Personally, I do use the Oxford comma, so this is wrong.
I should criticise though, we could not spell “responsibility” correctly on our $50 note (at least it was in the micro-text).
I use the serial comma too. 
Optional means you can use it or not. I had a English professor bust me for an optional comma error. Frustrated author stuck teaching football players how to make a sentence IMHO.
Living languages change from generation to generation. Thus Latin is still favoured for legal usage: being a dead language, the meaning of a term or phrase is likely to stay unchanged over hundreds of years.
This is what allowed the High Court of Chivalry to be reconvened in England after a gap of two hundred years, to settle a dispute about the use of a coat of arms. Everything written down in previous decisions stretching back over many hundreds of years was still usable to determine precedents, because the meaning of the language had not changed.
By contrast, in a living language the meaning and use of words, and the rhythm of the language in which they are used, are all subject to change as the shared understanding of terms and contexts changes. Formal language changes most slowly, because permanence and consistency are valued over subtlety and expressiveness. It’s no surprise to me that another dead language - Norman French - still has a place in British parliamentary proceedings for that reason.
Everyday English is constantly changing, especially in its most informal phases. A piece of slang that perfectly expresses a common feeling can feel ridiculously dated a decade later. Our everyday usage typically mixes long-lasting phrases with other more transitory ones to achieve the best expressions.
All the rules of English are inventions after the event, retcons made up to imply that the organic growth of the language always operated within them, when in fact this was never true. The same goes for spelling. Some of the best words in English were made up by writers needing an expression: try searching for “Shakespeare neologisms” to see how many just one writer coined. For a shortcut, try this article:
I always bear in mind an old saying passed on to me early in my life: “The rules are for the guidance of the wise, and the observance of fools”. I’ll use the serial comma if it clarifies meaning, avoids the accidental grouping of two items that should be kept separate, or gives the spoken sentence a rhythm that fits its meaning. But if none of those needs are present, then I feel no need to use it.
All the above is a very long-winded way of saying that I think the whole thing is a storm in a teacup. [Raises one eyebrow; moves on.]
Or perfectly innocent words are subverted. When I was young most children were gay, as were a lot of adults. Now if you say your child is gay, people will look at you funny or offer you their condolences… 
I like to use a lot of subverted words in their original context, just to make people think twice.