EXACTLY what I was getting at, you just said it better.
The sheep are the reward, and they can't get to them unless they do what you ask. It's like teaching a dog to "leave it", making him learn that he won't get what he wants unless he does what *you* want first.
I don't think harsh correction is necessary in stockdog training either, though with an extremely drivey, beginner dog I wouldn't be mortified if someone gave a yank on the long line for a serious offense. In many cases, I've noted that this is a far less severe correction to the dog than removing them from the sheep entirely.
I'm planning on sending my Eve out for a month or two with a professional trainer to get her started. I would never send her to someone who uses harsh correction, e-collars etc. however, if he thinks stops and humane correction on a long-line would heighten her awareness of what she's doing, I wouldn't be opposed to it.
All the right moves are usually already in the dog, it just takes some refinement through training (and yes, correction, whether it be in the form of verbal markers or physically stopping the dog) in order to bring them out.