4,
I don't think liniman is saying it's a bad thing. It's just a bad thing if you're playing the retriever games. Both examples are successfully used in a hunting scenarios.
The notion of handling your dog to an area is something that definately works in a real hunting situation. So does sending your dog on a line where he's going to come into contact of scent of the downed/crippled duck and then use his natural instincts to track it down.
I think what the NAVHDA duck search shows is that in the event you don't know where the duck is, or you marked the fall poorly and despite handling or sending the dog on the wrong line; that the dog will have the desire, purpose and cooperation to realize he's been sent down a wild goose chase; expand his search and work until he finds the game. Is it a good thing to evaluate? Absolutely. Is it required in everyday hunting? That's probably on the fence for the average hunter.