"I think you would have to keep one to appreciate the difference."
That is so true! I own seven dogs (they're pet dogs, I don't have a kennel -- yes, I'm crazy).
I've read a lot about the breeds I own (and about almost every breed, in fact). But you just don't know what the difference is between this and that breed until you live with them.
If you have only one dog or one breed of dog, you will most likely think of them in a positive way and find them far more intelligent and smart than other dogs you see on the street or at a friend's house.
However, when you own -- or have owned over the years -- more than one breed, you can see what we mean when we say that Border Collies are more intelligent, that Great Danes ar lazy, that Newfs are gentle, that Shih Tzus are ... uhm... not as intelligent. Et cetera, et cetera.
Besides the dogs I live with (Border Collie, Dane, Newfoundlands, Berneses, Dobermann, St-Bernard), I also happen to work with dogs every day. I see different breeds and different owners all the time.
Yes, a Pekignese living with a nice person can look far more intelligent and pleasant than a Border Collie stuck in a cage for 20 hours every day. But still, you can see some attitudes, some behaviours that tend to show more in certain breeds.
And yes, I think it's fair to say that some breeds outperform other breeds in certain (or all) type of activities. And it is clear some breeds are more intelligent that other breeds, will learn faster, will learn more, will work harder, etc. However, these breeds REQUIRE work and activity. In the wrong hands, they will look just as dumb as any other dog...
It's just VERY hard to see and admit these differences when you own a single dog, or when you prefer a breed over an other.