As Apple vet every application before it's allowed on the store, it would be easy for them to reject an app due to incorrect sound usage so the developer has to make sure the sound functions correctly.
As Apple are, by their own choice, policing the App Store it is there fault for letting Apps that don't work correctly into the store.
It's impossible for Apple to test every single thing, there are many things that they miss. We can complain that they're not being strict enough but then apps would also take a lot longer to be approved.
And at least as far as the iPad goes the switch is still a rotation lock since 4.2 is not officially out yet. Developers might still update their apps with the correct behavior.