I run a lot of IRCA registered internal QMS auditor training courses and part of the objectives for this course state that the delegates shall be able to:
Describe the responsibilities of an internal auditor and describe the role of internal audit in the maintenance and improvement of management systems
For me, the requirement to maintain and improve the QMS is essential to the role of internal auditing. If this function is not in place we would be relying on the 'good intentions' of inspired individuals to ensure that the QMS was kept current and was improved upon.