Furthermore, CMMI is just a model, it's not reality. Like any other model, CMMI reflects one version of reality, and like most models, it's rather idealistic and unrealistic -- at least in some ways. When understood as *just* a model, people implementing CMMI have a much higher chance of implementing something of lasting value.
As a model, what CMMI lacks is context. Specifically, the context of the organization in which it will be implemented for process improvement. Together with the organization's context, CMMI can be applied to create a process improvement solution appropriate to the context of each unique organization.
Putting it all together:
CMMI is a model for process improvement from which (astute) organizations will abstract and create process improvement solutions that fit their unique development environment