@paulsalter: I know that Kobo is working to standardize, as much as possible, the experience folks have using the various apps. They now have one senior staff person who is responsible for all of the app teams who who also has that responsibility. Things are bound to get complicated when the various OS developers make changes without checking to see how convenient it is for their competitors.
It probably doesn't help that the play store is not inclined to let developers make available different versions for different OS releases of an app and that the sea change that the 4.x releases were make backward compatibility a huge challenge (or entirely undoable if you want to really build out for the newer versions).