Of course Org Mode is completely different, because it can do tons of other stuff. But among it's many features, it also has lightweight markup syntax about which you could claim "if you follow these conventions when doing ASCII art formatting, the my program can transform this to HTML or whatever other format". And the conventions in Org Mode are also email-like in the sense that they don't look out of place in something meant to be plain text. (Maybe finding some large email corpus could answer which syntax is more email-like between Org Mode and Markdown, and maybe Markdown wins on that front, but my point is both syntaxes are lightweight for the most commonly needed markup.)
