Pit Bulls have a pretty high prey drive, as do most terriers. As far as Labs go, they aren't really supposed to but there are SO many careless breeders out there you can really get anything from a Lab, BYBs only care that their dogs are "nice family pets", are adorable, or make them money. Temperament beyond "doesn't try to eat the kids" isn't really evaluated.
I do agree that TONS of dogs will chase cats in their yard, regardless of breed. Max would always try to go after cats in the yard, was absolutely an angel when we actually got cats. Outside when they were running in an open space they were fun toys, inside the house they were family.