I am unable to quit out of most apps. I have tried depressing the Oculus buttons individually and together, and I have also tried the B and Y method. The only thing that gets me out is to use volume/on button method which limits my options to shutdown or restart.
As far as I know you can always use the Oculus button on the right hand controller (a short press) to get back to the lobby and there you can close the game. It's not the prettiest of user interactions but it works.
One thing to be aware of is that the Oculus buttons are inactive if you move the controllers a lot. So keep the controller still while pressing the Oculus button. This can be deactivated in the settings.