According to the official Android design guidelines, the Up button should take the user one level up in the app hierarchy: http://developer.android.com/design/patterns/navigation.html
I have a question about the Up button behaviour for this hierarchy of screens in Google Play:
Where "Up -->" means "tapping the Up button here takes the user to..."
Google Play (no Up button) - Apps (Up --> Google Play) - Staff Recommendations (Up --> Apps) - Monster Pet Shop (Up --> Apps)
I'm wondering why tapping the Up button in Monster Pet Shop takes you straight back to Apps, and not to Staff Recommendations. I'm going to offer my own interpretation below, but I'd be very interested in any alternative views.