alt Hacker NewsMarkdown without formatting isn't usually the nicest to read imo. I actually appreciate a well laid out and formatted document myself.
Also wysiwyg doesn't mean it can't be back and forwards compatible with markdown, it might just mean that it's a markdown editor gui with a preview.
It’s also not nice to write longer text in monospace. Or to have long URLs interrupt the text just because you want a hyperlink on some word. Or having to lay out tables by hand like ASCII art. Seeing *this* isn’t the same as seeing this. And you need custom editor software anyway to have affordances like TOC navigation.