The typical user doesn't care about updates. Most iPhones I see have 15+ uninstalled updates. The response to every Facebook update shows that that the typical user will resist change. Why would silent updates be critical to these kinds of people? I can about what version they are on as a developer but they don't care.

The back button is useful to some apps, some of the time. Why should you show it all the time and confuse users? Native back buttons also allow you to show context; you can display information about where the back button takes you.