Once a post has been edited once, there is a direct link to the revision history of the post that is visible to everyone as in this example:
However, when a post has not been edited, this link is not directly accessible. The revision history still exists: one has to manually change
to access it.
Admittedly, there is little point in doing this when the post hasn't been edited. However, for the purpose of transparency, it would be useful to have access to the post history even if there is nothing to see. In fact, for the purpose of academic citations, which is of great interest to MathOverflow, it would be best to have access to direct links to specific versions of a post.
Moreover, non-edit actions such as open/close and delete/undelete history cannot be seen without doing a manual url change. This is in opposition to the moderation transparency that MathOverflow seeks to have.
Remark (added on Oct 4, 2015): This feature request is still pending.