Why do Samsung and Google keep fighting?
I think you got it right as to why. But I think it's not so much war but healthy competition they accept for mutually assured growth. Down the line, I can see Samsung breaking free from Android OS and developing it's own OS, perhaps with the ability to use Android apps that may be compatible with the OS, as Microsoft Apps are. It may come down to this. If google continues to grow as a hardware developer it may want to not share android with Samsung and Samsung may feel the need to break free from android.
I also find Apple's dependence upon Samsung for displays OLED, to not be good for business down the line.