If a company does ever manage to fork AOSP, clone the Google apps, and create a viable competitor to Google's Android, it's going to have a hard time getting anyone to build a device for it. In an open market, it would be as easy as calling up an Android OEM and convincing them to switch, but Google is out to make life a little more difficult than that. Google's real power in mobile comes from control of the Google apps—mainly Gmail, Maps, Google Now, Hangouts, YouTube, and the Play Store. These are Android's killer apps, and the big (and small) manufacturers want these apps on their phones. Since these apps are not open source, they need to be licensed from Google. It is at this point that you start picturing a scene out of The Godfather, because these apps aren't going to come without some requirements attached.
While it might not be an official requirement, being granted a Google apps license will go a whole lot easier if you join the Open Handset Alliance. The OHA is a group of companies committed to Android—Google's Android—and members are contractually prohibited from building non-Google approved devices. That's right, joining the OHA requires a company to sign its life away and promise to not build a device that runs a competing Android fork.