It is more than just that. Log files only give you a list of individual transactions that happened. Auditing capabilities (as I understand them) imply the ability to trace a sequence of interrelated transactions in order to determine whether business procedures and rules were properly followed or even determine flaws in the procedures and rules themselves. For example, if a customer complains that a physical product is defective, and you detect that a specific component is at fault, you could trace which supplier sold you that component, when it was bought, where it was stored, etc., in order to determine the root cause of the component being defective: Was a business procedure not properly followed? Is there a flaw in the purchasing/storage/manufacturing/whatever process that results in products being defective?

That sounds way more comprehensive than most "auditing" I've seen in software. Usually it's timestamped activity logs with a couple of reports and maybe some filtering. Very basic.

Well, then software salesmen are taking advantage of the ignorance of their customers.

Of course, "auditing" as I described it is not just a button to be clicked on a GUI - it requires the user to know what stuff he is auditing in first place.