[rizwan]

UIViewControllers fall somewhere between an Activity and a Fragment.

In particular if you use any kind of view controller containment (custom container view controllers), you can only do that with fragments, and only then with Android 4.0+.

As someone who's looked at building tablet apps, the containment is a good thing to consider. In these cases, iOS makes it easier to combine your existing view controller hierarchies, while there are some idiosyncrasies (only 1 action bar across the top of a "split view controller") on Android still that don't always make things easy (in my opinion).