How to determine the rotation direction, rotation angle and rotation speed of a stepper motor and a servo motor
For cheap and plain RC servos you are right, they control their speed and rotation themselves. The user specifies a certain target position with a PWM signal, and the servo tries to transition into that position. 
It depends on the servo how fast it will move, e.g. you can't be certain about the speed. You can't even be certain if the servo did ever got into the target position, but it will try to get there as hard as it can.