Eh, I don't think a post-mortem is really necessary. They said it was a broken code change on the status page. If they wrote a post-mortem, it'd probably just say "A team member forgot to foobar the bazqux when deploying an update. We immediately followed our playbook for rolling back a failed deployment and restored service within 9 minutes."
Given the increasing dependence on messaging platforms, I think any widespread downtime deserves a public post-mortem.
And that's not to speak to the amazing amount of curiosity and interest that any downtime in a large public system generates. From the PR side, I would think that some kind of post-mortem is almost necessary to prevent that curiosity and interest from turning to distrust and negative perception.