
The issue is not necessarily the standard saying you can scissor, so much as not saying that your dog will be penalized if you do trim it. In the case of the Setter, the AKC standard may enable trimming a bit more by saying that the coat should not affect the lines and movement but nowhere in either standard does it say that the coat should not be trimmed. That's the beauty (or the danger) of standards being left open to interpretation I guess.
Here are the breed standards for the English Setter:
AKC- "Flat without curl or wooliness. Feathering on ears, chest, abdomen, underside of thighs, back of all legs and on the tail of good length but not so excessive as to hide true lines and movement or to affect the dog's appearance or function as a sporting dog."
KC- "From back of head in line with ears slightly wavy, not curly, long and silky as is coat generally, breeches and forelegs nearly down to feet well feathered."
The AKC's coat description for the Springer is quite a bit more in-depth though. It specifically states that the dog may be trimmed but not overtrimmed whereas the UK standard says nothing at all about trimming. Left open to interpretation though, the AKC standard says trimming is ok and different people draw the line between trimming and overtrimming in different places.
Breed standards for the Springer:
AKC- "The Springer has an outer coat and an undercoat. On the body, the outer coat is of medium length, flat or wavy, and is easily distinguishable from the undercoat, which is short, soft and dense. The quantity of undercoat is affected by climate and season. When in combination, outer coat and undercoat serve to make the dog substantially waterproof, weatherproof and thornproof. On ears, chest, legs and belly the Springer is nicely furnished with a fringe of feathering of moderate length and heaviness. On the head, front of the forelegs, and below the hock joints on the front of the hind legs, the hair is short and fine. The coat has the clean, glossy, "live" appearance indicative of good health. It is legitimate to trim about the head, ears, neck and feet, to remove dead undercoat, and to thin and shorten excess feathering as required to enhance a smart, functional appearance. The tail may be trimmed, or well fringed with wavy feathering. Above all, the appearance should be natural. Overtrimming, especially the body coat, or any chopped, barbered or artificial effect is to be penalized in the show ring, as is excessive feathering that destroys the clean outline desirable in a sporting dog. Correct quality and condition of coat is to take precedence over quantity of coat."
KC- Coat: "Close, straight and weather resisting, never coarse. Moderate feathering on ears, forelegs, body and hindquarters."