There are a number of elements supported by AsciiDoc that aren't available in Markdown[0].
For most writing, Markdown is perfectly sufficient. If you're doing complex stuff, however, AsciiDoc might make expressing your intent more straightforward.
I didn’t remember any of that from the article so I went back and checked. Seems that although you’re absolutely right, the article doesn’t give any details whatsoever other than obliquely hinting at it somewhere towards the bottom of the article.
Thanks for the comment, it actually seems quite a bit more interesting now.