Markdown is ubiquitous because it is easy for humans to read and write AND enough humans used it to make it so.

The second part is more important than the first. There could be far better systems which not enough humans used to make ubiquitous. And as far as we know, markdown could be one of the worse ones, but became ubiquitous because it became ubiquitous.

cf: MS Windows.

I don't think Windows is an apt comparison. One had huge market forces and distribution channels propelling it, the other is a description page, not even a standard, on Gruber's site.

What Gruber got right is that the syntax is beautiful to read, easy to write and powerful enough to be useful, with the optional inline HTML as an escape hatch. It may not seem much, but that's hard to get right.

Agreed. Personally I really like asciidoc but hardly anything supports it. Markdown is just everywhere. In all the tools I use and all the most popular tools available. So it's far easier to use when it's so portable. So I only need to remember one set of operators to get the results I want. Even in systems where I don't know which syntax they support. There is a good chance Markdown is will be one of them.

you're both wrong.

markdown is ubiquitous thanks to github.