[stickfigure]

Markdown (like HTML) offers formatting structure, not semantic structure. Maybe you want to query for recipes that can be made in under an hour, or that contain orange as an ingredient (as opposed to merely a serving suggestion in an orange bowl). A proper XML (or even JSON or YAML) structure would enable this, Markdown does not.

You can pretty easily translate XML to Markdown using XSLT, though.

I don't think hierarchal structure is the differentiator; recipes and web pages are hierarchical and they'd still be hell in JSON. XML handles hierarchy just fine. I think the differentiator is whether your content is a document, that is, composed significantly of multiline text. Multiline text in a JSON file tends to be human-hostile, but we're all comfortable editing eg html.