Ask HN: Why no preview and no ninja edit on HN?

Given how everybody on HN is constantly praising "agile", TDD, "fail fast", "incremental changes, etc... I'm surprise there isn't a preview or a ninja edit (ability to made and edit for x minutes after a post/comment without showing as an edit) on HN.

I see the preview functionality as the posting equivalent of TDD, and ninja edit as the posting equivalent of Continuous Deployment.

I always get the little formatting that is available wrong, and find the fact that you can only get one go at writing your comment without being marked as "edited" at odds with modern software implementation methods.