You are right that auditing is "missing" in WCM.
The justification is that WCM is based upon the AVM stores which are fully versioned by design. So you can always see who did what, when for every file in every revision.
I chatted with my Alfresco colleagues today and we agree that this is a low priority issue that needs fixing sometime. If you feel strongly about this then please raise an issue in JIRA.