Easy once you understand that governance has nothing to do with management, despite the way the word is abused by vendors and analysts. Governors don't do, and they don't measure or report or audit or manage or secure or check, at least not while they are wearing their governor's hat. For more see
http://www.itskeptic.org/node/508
The new standard makes clear that governance is about telling the doers how to do their job, not about doing. ITSM tells us how to do the delivery bit. ISO20000 measures if we are doing it. The governors will be interested in the feedback of an ISO20000 audit because it measures their subordinates who are doing it.
Governance is above management. Management is above doing. Nowadays doing is called "management" anyway (Change Management, Incident Management...). Let's not start calling management "governance".
Less crudely the standard defines that (IT) governance is about Direct, Evaluate, and Measure. Direct means set policy, decision rights, strategy... for those who do the doing. (the "measure" bit is about looking at numbers produced by do-ers, not about doing the measurement). It sounds to be a good standard, I'll be getting a copy.
the
IT Swami predicts that future IT Management will be about three integrated things; Service, Governance and Assurance, where Assurance includes compliance, risk, audit, security...