Narcs cannot communicate at any deep meaningful level so they resort to the silent treatment and ignoring. Communicating authentically would mean they would have to acknowledge some of their shortcomings and they're not about to do that. They are cowards and spineless. Yes, it's part of who they are. Just another behavior that indicates they don't give a fk...if it's not about them, they don't care.
Ignoring is another form of abuse; the message being, "what you have to say is not important...you are insignificant."
Here's a good article about silent treatment and how it is deadly to relationships:
http://powercommunicating.com/
Silent Treatment is Abuse