The post-mortem process can cover all of these things:

  - what happened
  - impact
  - root causes
  - what will be changed (commitments)

You can't really talk about what to change w/o talking about root causes, and you can't talk about that without talking about what happened. You also can't consider the costs of commitments to be made w/o discussing actual and potential impact because resources are limited and the cost of opportunity is real.

It's fine for executives to get only a summary of impact + commitments. But the whole post-mortem process has to be followed, and some people have to be aware of all the details.