Authentication is easier. Application access becomes simpler as well, since even a JS tool running on a browser can connect and check your site. That also means not running an additional S/FTP server, which frees up resources to serve content (which would include responses to API requests).
Plus you get more fine-grained control of exactly which features are displayed to applications and this could include number of hits and other statistics (if they chose to implement it).
... like FTP?
I guess I'm confused why reinventing the wheel here is necessary when you're going to end up with a HTTP tool with the same semantics.