You could be forgiven to have thought that Facebook and Google had put aside their rivalries and become BFFs after the launch of Facebook Home and the HTC First. However, it didn’t take long for one side to strike the other, with Google making the move to update the Play Store policy and ban developers from bypassing the official update mechanism.
Facebook opened a can of worms when they added a feature in one of their latest releases that allowed them to auto-update their app on certain users’ devices for beta testing purposes. I remember getting the option to enable it and being absolutely flabbergasted that they even considered it OK to do so (if it was opt-out with no information shared, I’d probably have quit Facebook entirely despite my sister now working with them).
No app should have the right to do so, and Google probably thought that they wouldn’t be able to until the Facebook did it. My guess is they had their lawyers have a look at the policy once more to make it watertight. Facebook, your move.