BBC (I think or maybe it was PBS|NPR) did this. Recent article talked about how they decided to go "open" and put everything in API. Later on when developing for satelite stations and other projects they found using their API was the bestest, fastest way to go.
"If you haven't built your website on top of your API, consider doing that -- or at least what it would be LIKE to do that. If your API couldn't reproduce your website, your API needs fixing."
At first, I was going to argue with this. But then I realized: You don't have to actually -do- it, just write like you would. You don't have to give third parties the ability to do everything you can do locally, so long as you program in such a way that it can be done. It helps decouple things better, and make things more testable.