As much as I like vi's interface, I think emacs implementation is superior, and org-mode invaluable.
Why use org-mode as a format instead of Markdown? Internal cross-references. Org-mode feels just as light weight to me as Markdown for the most part, but it has fewer cases where you can't make things work. Worst case in org-mode, you mix in LaTeX.
Etc.
I think I still prefer to just write it in markdown. Word can't come close to the typesetting ability of LaTex.
I think the biggest difference there is that a document is "static". It is not supposed to process something else like code is.
Thus what you want to avoid at all costs is "boiler plate" bugs. Bugs that are not caught at compile time because it is semantically correct, but that end up producing wild results once a certain kind of data is introduced.
Microsoft Word's binary format (.doc) stored the document's text as a block in the file, making data recovery simple.
In general, plain text is great because it's explicit. In contrast, word processors store some odd chain of objects. The steps to rebuild a document from scratch that leads to the same representation are not totally obvious. Sometimes it's a bit stochastic even!
XML formats improved the situation, but still plain text wins IMHO. With plain text you can have a toolchain where components for version control, edition and transformation can be replaced seamlessly. New stuff can be introduced at will. In e.g. Word you're mostly locked-in, or at least it's far from trivial to break out.