Why the back ends?

While talking with a colleague on a UX training program to be given to the internal staffs, a question was raised: why the backend? What has the backend, specifically the middle-ware to do with UX? I told her, the answer is simple, the data presented and accepted by the middleware will affect how information can be presented to the users as well as the possible or allowable interactions. A badly designed middleware will put too much constraint on the UI and severely limit the ability of the interactions, creating a bad user experience in terms of performance (too much post-processing) or usability (too much unnecessary user interactions).