Aleron, I suppose to answer your question I think the issue lies in focus. I'm not sure about working breeds but a lot of sporting breeds seem to lack the type of focus BCs have. It's kind of hard for me to explain, I love a lot of sporters too but I have a feeling that they are rather scattered for quite a long time until they really mature and get into it which doesn't seem to happen very fast. Most BCs I know appear to have a kind of intense focus even as young 6 month old puppies on the task at hand be it agility or trick training or whatever.
Obviously training matters too but there's a reason why so many top obedience people have Obedience/Performance bred Goldens.