> That’s just a bad syntax choice on Gruber’s part.

I believe Gruber was inspired by how people wrote emphasis in plain text emails and other text documents. Most MUA at the time would treat trailing whitespace as a hard rather than soft line break. This is from my--now aging--memory, and I can't find a source to corroborate. I do recall, though, there were clients that didn't do it well (ahem, Outlook), and would break plain text formatting of deeply-nested quoted text. (Don't even get me started on how Outlook single-handedly changed culture from bottom posting to top posting).