TDD for product dev: Where we're going we don't need... roads

"At the end of the year they took an aerial photo and the tread-worn ground became the blueprint for the optimal sidewalk routes as chosen perfectly and implicitly by the student body."

I still think this was genius.

However, I don't see how it applies to software development. Do you publish an API that makes it possible to do -anything- with your system that is imaginable? How would you do that, direct SQL access? Anything less than raw access would mean you were building a LOT of sidewalks, then removing the ones that weren't used.