Take a look at any blog, wiki, forum, etc. Specifically, look at how posts are created, filtered, and displayed. There are dozens of different ways for authors to specify the formatting and content of their articles/posts, and hundreds of ways to render the results. Some blogs rely on now-famous 3rd-party markup implementations like Textile and Markdown, some use bbCode, and quite a few still rely on plain old HTML. Then you have vendor-specific proprietary implementations and many more, popping up as the need arises.
We’re not trying to standardize markup formats, on the contrary, there is no real benefit – and the web can always do with a bit more diversity. But what does need standardization is how post-markup data (the article text) is stored in the database and later rendered. In the past, this wasn’t a problem: each “platform” had its markup format, and stored the output straight in the database. Then the platform triggered the markup language’s bundled HTML renderer and converted the database contents to HTML for display.