This was brought up back in 2012, but I would like to revisit the question again, if possible.
Should questions about apps be allowed? The consensus in '12 was that the community wasn't very large, so it was a way to have more users. However, I think the community would perhaps be large enough to do this now. Additionally, the app-specific questions I have seen seem like they all tend to go pretty much the same:
Comments: "Have you tried restarting?" "Is your phone up to date?" "Check the Store for updates?"
Answers: "Restarting my phone fixed it for me." "Me 2..plz fix me dude thanks." "Try turning the flashlight on. (Or some other equally unrelated answer.)"
As such they tend to feel quite low-quality, IMHO.
Personally I would vote we take one of three actions:
1) Close app questions that seem to have no relation to the OS (e.g. this one), and point them to the developer for support.
2) Require that the question include the app version, OS version and model of the phone. This would allow us to immediately know if the app needs updated, the OS needs updated or the app simply doesn't work correctly with the phone model. (Though this may be a bit hard to enforce.)
3) Put a full-screen popup on the site's home page that says "HAVE YOU TRIED RESTARTING YOUR PHONE?"