You have to remember, I work in an industry that does many projects in-house, from Surveillance to construction to IT projects. And although we do have an Integrator performing our system replacement/update, it's primarily due to my team not having competencies for certain aspects of the job and having a relatively small team.
Under other conditions, I would seriously consider performing all or most of this project ourselves. In fact, we do more in-house than some even larger casinos. I don't see that as any different from a city utility department doing their own install. In fact, my hat's off to them.
Despite the flack I'll probably receive for this, I don't think Integrators have a monopoly on installation competence. Some are better than others and some are worse than many end users. It all depends on the skills of both parties and the dedication of the end user. Some of us actually take pride in keeping as much in-house as possible.
As for one department billing another, that is an accounting thing. It allows them to jibe expenses with department budgets.