Per the forum guidelines: http://codex.wordpress.org/Forum_Welcome#Deleting_.2F_Editing_Posts
Users can edit a post for up to 60 minutes from the time of submission. After that, the post can only be edited by a moderator.
It is not the general policy to edit or delete forum posts. When a post is made and people contribute answers to an issue, that then becomes part of the community resource for others to benefit from and deleting posts removes this added value. In extreme circumstances, members of the moderation team might be persuaded to remove sensitive information that has been included in posts accidentally – but your best course of action is not to publish anything that you wouldn’t want to be public. (Remember too that other sites take archive copies of the forums, and we can do nothing to control that.)
tl;dr: We don’t unless there’s a good reason. If you don’t want your link on the net, don’t post it.
