That is for a servo modified for continous rotation and not an unmodified servo.
Yeah, I think I made a big mistake. My first comment should have been "is it a regular or modified servo?"
Apparently, it's regular, which is why the for-loop works.
The only way to control the movement speed of an unmodified servo is to keep updating the position values
every 20-msec or so. IE, interpolation, (start_pos - end_pos)/velocity = pos_increment per unit time.
That's probably what the long thread pointed to talks about. Either code this into the Arduino, or as indicated,
use a servo controller with this feature built-in.