Um, its worth nothing that ActionBarCompat is not an addition to 4.3. Its an addition to the support library. If you include the support library in your project and you can use features from 4.3, such as fragments, and the action bar all the way back to android 1.6. The support library is a backport of modern functionality.

This is part of googles approach to addressing fragmentation on the Android platform.

Small correction, the support library which has ActionBarCompat only goes back to 2.1 (each version has a number representing the API version it supports, in this case v7)