Right... Herding and retrieving are both prey drive, the dog has merely accepted that he's not hunting for himself, but for his leader.
Funny story... I watched a corgi (also a herding dog) in a 4H obedience show, biting the legs of her owner repeatedly during the heeling exercise... the dog wasn't heeling her, he was herding her :~D
nip nip nip
At least Corgi's are small...