This is something that some friends and I have gone around and around on more then once.
First off, if I order birds that are simply for running about and laying eggs, I still expect them to look how they ought, even if they are not the perfect picture of a show bird. Barred rocks looking like barred rocks, and I'm very picky about the shade of "rhode island red" the hatcheries throw me. If they are not the dark red colored birds like my mother and grandmother raised they usually get sold as "sex linked reds" even if the invoice says "rhode island reds". When I raised silkies if I got a 4-toed bird regardless of how good the parents were i sold it local as a silkie cross.
Now with show birds, there are several instances where I truly think a secondary standard has arisen. The Modern Game came out of trying to please the judges years ago when the Oxford Old English were first entering the show ring. Cornish look entirely different now, to the point where I've seen many calling their more rangy homestead-type Cornish "Indian Games" to differentiate them from the bulldog-like cornish in the show ring.
As was stated, some traits are hard to spot in the show arena - "how well does that best of variety Leghorn hen lay?" But some are more visible. Breeds that were once hardy free-rangers have become powderpuff couch potatos, roosters that were once fierce warriors have become squalling sissies. I believe show people, preservation and heritage people, and even the backyard flock owner should all try to work together to bring an overall uniformity back to the breeds of their choice. There's always stubborn ones in each group though; the "righteous crusader" heritage breeder who ignores either partially or entirely the standard looking only to make the breed functional again, the "aristocratic" show breeder who doesn't care how well the bird lays or survives cold temps, so long as the bird wins the shows and thus proves that it is superior to what everyone else has. Not all members of each group are like this, but some are, and unfortunately it causes rifts that make bridging the gap more difficult.
I feel I've wandered....back to the original question. I feel that every breed has what I call workable defets. We all know that not every single specimen is perfect or even close. A breeder, regardless of their aims (show, preservation, just to sell some birds to the guy down the road - and in fact we should try to be a little of all three) should put forth the effort to learn about their chosen breeds enough to recognize these workable defects. These defects are not major and can either be bred out or used to improve your stock. Not all show fowl are broodfowl and not all broodfowl are showfowl. A breeder should also recognize that if a lot of these defects show up or a defect shows up too often that those birds are not properly representing the breed they claim to be. Once a flock of a particular breed fails to meet the temperment, production, vitality and physical standard for that breed more often then not - that is when a person needs to reevaluate what they are doing with their stock and whether the stock they have is worth propogating. In short, if the birds don't measure up at the very least the majority of the time in all aspects they no longer are that breed.
