Yoav's murders of Avner and Amassa exhibit the simple act of dishonor to the king, and also jeopardize the prospect of national peace and unity. Yoav's bloody ways characterize the reign of David but are not appropriate for the peaceful reign of Shlomo.
Shimi Ben Gera's venture to "Akhish ben Ma'akha, King of Gat" may be hinting that this is a venture of political maneuvering on Shimi's part, an appointment with a rival king and not a simple return of slaves.
The description in Divrei HaYamim of the transition between David and Shlomo is formal, regal, ceremonial, public, and sedate in contrast to the description in Melakhim.
