I'm not claiming you claimed it was a simple specification :-)
I just find it interesting. This would indicate to me that there are 500 "features" in the language. I thought mark-down languages just provided a few shortcuts for producing the most commonly needed HTML features and then provide a fallback to HTML. So if you cannot do it in the markdown language, use HTML instead.
Why would I care if one is merely “formatting” or not? If I have to run a tool either way, I would prefer one that accepts a user-friendly input language and decouples content from presentation.
Because transforming an .md file into an .html file is a lot more invasive (though taken for granted here I think) than just writing the .html file. It's a build step where there wasn't one before.