Yes, a good programmer writes a robust application, but ignoring the specifics of this case is being entirely disingenuous. If I write an app to use the Play API and only distribute it via the Play Store then there is no good reason for me to spend my time writing `if (foo != null)` all over the place to placate someone trying to circumvent the official way of downloading my application.

You have to balance the tradeoffs of bloated code and pointless error checking with adding features and improving the program. The more error checking code one writes the more one must maintain and the higher the potential for bugs.