This is not totally true. Andoid itself is very much open, you are correct. However, there is a significant portion of userspace applications and services provided by Google that ARE NOT OPEN AT ALL, and are heavily depended on by the majority of the Android ecosystem. That is what it looks like this project is trying to address.

If you've ever installed a 3rd party distribution of Android based on the open source project (AOSP), you know how hamstrung things are after a fresh install until you drop Google closed source apps in.