Some Scottish Terriers don't chase cats, but most have a strong prey instinct.
You buy a Standard Poodle that is dumb as a post or a Pug that constantly makes a horrible high pitched barking sound. Wait a second! Didn't the dog breed book say Poodles were incredibly intelligent and Pugs made virtually no noise at all?
If you've ever ended up with a dog that doesn't exhibit dog breed characteristics, then you already know what many prospective dog buyers are about to learn. These characteristics are a generalization about most dogs in a specific breed, not a guarantee that your dog will act in a certain way.
Tthe loving owner of a Scottie who wouldn't dream of chasings kids or kittens will be pleased that his or her dog doesn't exhibit typical Scottish Terrier behavior. The owner of a Labrador Retriever that is terrified of water? Not so much.