Rich, I agree with all your points on apology. I would like to add one point for small business owners. If a mistake occurs and a client/customer complains to an employee, the employee should inform the business owner...and the business owner should express the apology (correctly, of course). It makes a difference "who" is expressing the apology, too. It sends a genuine message to the customer/client that you (the business/business owner) really care about making them happy and satisfied.
@TheRelationshipInsider Good point Sheryl, and one that has an important cultural context as well: in some parts of the world, having a senior person present the apology is considered an necessary sign of respect. Thank you!