Here on SO you need to know Markdown. On most other forums there is BBcode, or HTML.
It strikes me that this is considered good practice among developers.
Personally, I think it is bad practice. Basically, you are saying: We cannot create any decent WYSIWYG UI to edit comments or questions. So, learn our language or do not use such a language at all (and don't use any markup).
Shouldn't we as competent developers provide the user with a decent UI, so the users are not required to know such a language?