It is a little surprising that Steyn will play in the CPL but not in the ODI series. But I understand the need to rest him for the Test series, he is not getting any younger and has been set back with injuries as of late. He also hasn't exactly set the world on fire in limited overs in recent months.
Rilee Rossouw somehow keeps his place in the squad despite going through a torturous run of form as of late. I know he is still young, and South Africa's batting is deep, but thought that was an area they would have looked to upgrade.