Differences between APIC-EM and Prime Infrastructure 3.0

• Both PI & APIC-EM offer plug and play services as well as API programmability.
•  why should I also invest in APIC-EM. Does APIC-EM provide capabilities that cannot be achieved using PI.

PI 3.0 is built upon APIC-EM in the sense that it uses the APIC-EM controller to facilitate its PnP service. Is this valid to say.. Also if this is true, what is the true difference between both and what is the value of APIC-EM if Prime Infrastructure somewhat covers the major scope of what the average network administrator desires..

It is true that PI now uses APIC-EM for PnP.  In terms of differences, think of APIC-EM as a programmatic layer on top of the network (meaning you can extract things like topology, inventory, and network state programmatically).  Today, it does PnP, IWAN provisioning, and flow-based path trace.  All of these are also driven by a REST-based programmatic interface.  Think of PI as a network management application in that it does element, config, and fault management. 

What you'll see is that more and more network services will be exposed from APIC-EM that PI can take advantage of, so that PI becomes a set of applications on top of APIC-EM.

 while you can use APIC-EM without PI to do PnP today, PI adds a layer of value on top of APIC-EM in that it manages the config templates and software images, and uses the APIC-EM REST interface to drive the provisioning of new devices.  Without PI, you'd likely have to build your own application to do this management. 

In terms of investment, APIC-EM is freely available.  The IWAN feature, however, is cross-licensed with PI, so if you've invested in PI, then you have a license for the APIC-EM features as well.

IWAN is part of APIC-EM.  I did not mean to give the impression that it was not.  It is, however, a separate license.  You get this by default if you have Prime Infrastructure or a Cisco ONE software license.