This all comes down to how the servos are controlled. A conventional servo applies power to the motor that is propotional to the error in its position. For example; you commmand the servo to move 12 degrees, the air load is trying to stop this, in the end the servo moves less than 12 degrees. It might take a degree or two of error for the servo to generate enough power to hold against the air load. A digital servo on the other hand will command it self to near full power to get to the commanded position. This is why digitals are better, they go where you tell them to go, analogs only get close, they must by design travel short of the command when under load.

This is easy to see. Power up an analog servo and try to move the arm, try hard. The output arm will move a ways before it really fights back. Then try it with a digital, you can not move it. It is the nature of the two beasts.

Steven