...And that's not what a 'Customer' is.
I certainly understand where you're coming from, but I disagree on two points: How to serve customers and what a customer is.
1. If you're serving a customer in a way that involves conflict or opposition, you haven't served -- you've taken advantage of, even if your customer got something out of it. Businesses that operate this way don't tend to win in the market place for long.
2. If then define customer by who you serve (ie. the people you do something for), then people in an organization are very much the IT team's customers. The IT serves (or "does things for" if you prefer) other people in the company. In the same way, part of HR's job is to serve people inside the company.
I'd challenge you to change how you view customer. I think the best companies are those that partner with their customers -- not those that set themselves in opposition to them.