Amazon wouldn't be nearly as good as it is if it wasn't for the degree of software quality that they have.
In your customer service example IT has clearly had a positive impact, but you'd be hard pressed to convince anyone that the IT department is generating revenue for the company. If you walked into the CFO's office trying to make that case you'd be laughed out of the room. Good customer service does not manifest itself through good software.
A better approach may be to walk into the CFO's office and show how your IT department is helping the company realize it's goal of providing good customer service at an acceptable cost. It's a very subtle distinction. This is what I was getting at when I said not thinking of IT as a cost can be a roadblock to advancement.
Then again, I think it was Bezos himself who described Amazon as a technology company that happened to sell books too.