Re: APCC/APPM requirements for the Astro-Physics mounts.
There is, in fact, simple modeling provisions in the V5 Keypad and CP5 combo, presently being shipped with the Mach 2. We are working to make this available for the CP4/keypad combo. Here's some recent dialog:
The keypad provides a simple user interface, while the mount retains the database and performs corrections based on it.
To address your last question, realize that APPM/APCC runs on the host computer, and can interact with your camera and other software in ways that the keypad cannot. For example, APPM can initiate image captures and plate solves, which enables automation in the mapping process. This also enables model data to adhere strictly to constant-DEC lines, which offers performance advantages in some usage domains. Either APPM/APCC or the Keypad model can run passively in the background while using other third-party software.
The keypad model, in contrast, is intended to be ASAP (as simple as possible), with a small learning curve. It can be used with, but doesn't require, other computer software.