Chickens all have open studbooks like rabbits, right? So wouldn't the difference mainly be whether they are being bred "to a standard" or not? A hatchery can have both colorful egg birds bred in random pens and theoretically "pure" (for such as that definition can ever exist in animals with open studbooks, which I think it's awesome that they are kept open) examples of the same birds, but since they are breeding for egg laying ability over anything else, you usually get smaller, weedier-built chickens compared to people that care more about keel depth, tail set, etc. So they wouldn't be winning shows either way.
I forget if it's 4 or 8 generations, but I think with both rabbits and fowl (may be more livestock species) you can register it as a purebred after a certain number of generations go by... That's how we get "more" colors in breeds that don't currently have 'em. It causes a headache trying to breed unwanted traits back out, but that's penalized on its own just fine by judges adhering to standard.