(As a web developer) Yes, we frequently encounter Markdown on the web. Not just drafts, but often entire websites depend on it. Github is the largest community of computer programmers on the web, and all the communication there is written using “Github Flavored Markdown”, which, like it sounds, is just a variant of Markdown. (Markdown has many dialects, the same way English has many dialects… though Markdown’s are usually a matter of use-case specializations rather than regionalism).
Markdown is also widely used in the “content management system” space as a way for non-coders to easily write rich text to share with the public. Software like Astro (and others) makes it easy to turn markdown files into real webpages; there is a sibling discussion over at Which website building services meet these criteria? - #11 by Reply that briefly discusses this… (edit: but you’re already in that thread, lol)
Anyway, it is especially useful for teams of mixed coding ability; i.e. programmers can set up Astro, but the actual editors/academics/copywriting staff can produce all the content in Markdown.
From a programming/computer parsing perspective, Markdown is dramatically safer and easier to work with than HTML or XML, so it’s a good “common ground” markup language to use for basic documents.
It can. It doesn’t have to. It offers a “Canvas” feature that you can use if you want: Obsidian Canvas - Visualize your ideas
It is saved as a “JSON canvas” file format, which is not Markdown, but another open standard that Obsidian invented for this use case.