I know when i showed some calves and heifers at a fair, we walked them around in the ring and stopped them to have them stand in a particular position, and the judge would judge their conformation. Basically a conformation that is the most desirable for a milking cow.
So using what i know about cows.. for working lines they have a much different desirable conformation than that of show line, and than every breeder probably has particular physical traits that they find to be the most desirable and breed for those physical traits.
This is just my best logical answer. However, i really do not know very much about conformation in dogs!