When I hear this (and I do hear it all the time at the daycare) it usually doesn't mean 'this dogs breed traits can make them difficult for some people to own'. It usually means 'I don't have the time/inclination to train my dog to be a good companion, so I'm just going to blame it on the breed'. Some gems
Chihuahuas/Dachsunds/Bostons can't be housetrained. Ever. They aren't like other dogs
Pugs can not run, even in cool weather. They aren't like other dogs
You can not clip a Dachsunds nails without getting bitten. They have sensitive feet and aren't like other dogs.
A Basset hound can not live in the house due to it's odor. They aren't like other dogs.
A Pit bull has locking jaws/will turn on you/eats babies for fun. They aren't like other dogs.
Sighthounds will break their legs if you let them play with the other dogs. They aren't like other dogs.
English Bulldogs will all but vaporize the minute the sun hits them, even if it's only 55 degrees out. They aren't like other dogs.
You can't live with a coydog, they will climb on the fridge/dance on top of 10ft kennels/snatch birds from midair and start randomly singing with the ambulances at work. Oh, wait.....