I believe that user experience is not best thought of as an activity or function, but as a mindset. To varying degrees, every customer-facing person in an organization has an impact on, and, thus, responsibility for the user experience. However, if UX becomes the province of a department, others can ignore this responsibility, assuming that somebody else is caring for it. So then, the folks in the UX Department have to be explicitly vocal about what’s right for the customer, because no one else is focusing on it. But then the UX Department become something of the “customer police,” and other departments, in their desire to get things down, may try to simply route around the UX Department.