Interesting post by DD.
Except in the most unusual organizations (usually large, complex, and quite mature) change management practitioners often do not have the staff or ability to actively manage complex, ongoing change. Consultancies often bring in the right amount of expertise and headcount to actually help effect change in the organization. They also have an understanding of true change management that goes to the behavioral level, as opposed to sending out communications and training materials.I believe that traditional HR within organizations outsource both the very low end work as well as the very high end work.
Change Management outsourcing is a reality as organizations strive for objectivity and hiring an external consultant helps in maintaining that perception, no matter how impartial the HR head is.
There are some advice that are followed just because real money has been paid to get it.
It's all about perceived value.
Or as the Hindi saying puts it pithily "Ghar ki murgi daal barabar"