King David: An example of favoritism?

Let me start by saying that I am not worthy to call Kind David on anything.  I’m certain that the man after God’s own heart was more right in his life than I will ever be.  Having said that, my recent readings were a bit confusing.

We all are all aware that while King Saul was alive, even though David was anointed King, he refused to raise his hand against King Saul, even though he was fleeing him for his life.  Once Saul commits suicide on the battlefield, we see an amalekite claim that he killed Saul come and brag to David about it, and is killed on the spot because of David’s insistence on this principle.  We also see a repeat of this behavior when Saul’s son Ishbosheth is slain by Rechab and Baanah.

Between these two events however, Joab murders Abner in delayed retribution for killing of his brother.  While David mourned this loss, and cursed Joab and his family, he apparently did not execute any discipline on this close friend and general.

What do you think? Did he show too much favoritism towards Joab?  Was this an indication of difficulty dealing with his close friends, and later his sons?  How would we react in the same situation?  What would have been a better response?