I think they just vary so much compared to most breeds! You've got some people breeding purely for pets that are cute and fluffy and then the extreme opposite in that people are breeding for the elite elite agility levels. And everything in between. There aren't many breeds with quite that much disparity between what they 'usually are'. Not many breeds are bred to the level of performance some shelties are and the ones that are tend to not have as many dogs bred just for pets.