Originally Posted by Anabran
Honestly that depends,
are ALL android 2x apps automatically Android 4.1 compatible as of this writing??
Yes, apps that run on 2.x will run on 4.x. They may not look at their best as may not have been optimized for a large screen, but they will run nevertheless.
The only exception would be if an app were to use a non-public API which could have changed or being removed in a newer Android version, which would break the app.