Imagine you've got a small team responsible for a project. Say like ten people. They're basically taking care of the whole project, meaning they design, develop and deploy the application and do the O/S, database and infrastructure administration. And here's the question: how do you exactly enforce segregation of duties in such environment?
When you can afford expanding a team or having some interdepartmental administration/infrastructure/deployment/etc. teams, that's great. But sometimes the environment is too isolated and you just can't do that. In such case insisting on having a separate Tape Librarian person in a team is quite extravagant, if not stupid. So what should you do? Reasonably figure out what roles' separation is really important and try to enforce it. You will at least have some better arguments for it than just a usual "because that's the way it's supposed to be".