[Aardwolf]

Yes, Markdown is like HTML, its input is a plain text format but its output looks different (your single newlines get removed from the output, because single newline has a different meaning in the source code than in the output, unlike in real plain text, where they stay newlines)

> and plain text editor behavior, which many do not by default perform line wrapping

Not true, in a plain text editor you can make ascii art, or a dashed list of items, without having to type special syntax, and it will not become one long line

Dynamic line wrapping for display is something different than removing newline characters ("\n") you type in the string. Markdown does the latter. Text editors do not remove newlines you type.

> plain text email client conventions

I don't think plain text email ever removes a deliberate newline you type either. Does it?