As I know, most of robotic arms are specific-purpose and usually work under supervision of an expert, such as surgery robot. So, is this relevant for a robotic arm to be intelligent and autonomous? If so, how its control system may be different from non-intelligent ones?
I believe you are only noticing the robotic systems that get a lot of press coverage. Specialized, supervisory-controlled robotic systems are definitely not the most common. Check out this list of industrial robotic systems for quantities of general-purpose, reprogrammable, robot systems for comparison purposes. Whether or not reprogrammable industrial robots are intelligent is a matter of speculation and argumentation. It depends on your definitions of autonomous and intelligent.
At first it is important to distinguish between a Robot Control System itself and the development process to program such a system. A reasonable Control System is NREC Operator Control System which can control a robot arm. But a way more interesting is to program such systems. In most cases at the beginning is a teleoperating system, where a human-operator controls a robot with a Xbox-Controller. Than a parser is programmed for detecting actions. The next step converts the parser into a trajectory generator. Then, a time-scheduler follows and perhaps a sampling-based solver like DARRT.