Why can't I delete a Membership Status that has no memberships of that status
Ok, found it. If you have logging 'on' - and you have a membership which was at some point in history 'that' status - then when you search you find 'no results' - but there is a record in log_civicrm_membership

and presumably it is not be able to be deleted in case the record needs to be reverted.

If that is the issue, then perhaps the error message needs to incorporate that fact.

or should the membership status be ok to delete even with data in the logs?