I think that Suginami might have confused two things. There was a question about whether the throttle actuator is the same as the cruise control actuator. Suginami's answer decribed the control module, the electronic components, not the actuator. The actuator would be an electro-mechanical device that converts the throttle signal (generated by the module) into the physical motion necessary to actually open or close the throttle.
The link to the owner's web site correctly distinguishes the two devices (but does not describe the actuator itself).
To answer the question more directly, the control module and the accelerator actuator both do integrate the cruise control function, in contrast to earlier cars in which there was a separate cruise control module and a separate device (vacuum operated in at least some older models) that operated the throttle.
In my 300E, the throttle actuator is essentially a reversible DC motor that opens and closes the throttle. The specs say it can turn the output shaft from full open to full close in 150 milliseconds. In addition, it has a potentiometer to monitor the actual throttle position, and a safety switch. I am not familiar with the 500E throttle actuator, but presumably it is somewhat similar.
1992 300E with ASR
35 years of Diesels until now!