[necovek]

I took the original article on plain text to mean that you should aim for plain text formats which are human-readable even without specific tools to process them.

Thus HTML, Markdown and LaTeX make sense:

  \begin{document}
  Blah
  ...

Is completely understandable to a reader even 50 years down the line, even if they don't have LaTeX on-hand.

But, it does bring an interesting counter-point: what does $$\frac{1}{n}$$ mean (to not even bring up more complex examples). It's probably no surprise that LaTeX is the lingua franca of math input because it brings in terseness, simplicity and some readability to plain text. Still, it's a programming language, so literally all bets are off in a document (you can redefine \frac to mean something else entirely).

I guess both articles, as noted elsewhere, attempt to nail down one familiar truth: use the simplest expression possible, but not simpler. One thinks that's always plain-text except for images, but there are just more contexts where this applies.