Let me see if I can explain it better with the knowledge I've known and a bunch of emails LOL! If I am wrong or misinterpretation the standard, please chime in.
We Americans are more specific in what we want in our standards in Welsummers however for some breeders like Nate, want to keep the Dutch standard on his birds for his Dutch Welsummers instead of going "American". Just like Arabians and their heritage, some of us would keep our lines pure according to the origin they came from.
The British do not want too much brown in the chest (like the Whitmore roo pictured, having too much brown) or solid black with no brown feathers anywhere from the chest to back of his rear end. So 20 percent is more ideal of how much brown you want in a Welsummer. If you want German or have German Welsummers (correct me if I am wrong!) are a bit darker, more richer in color than the Dutch Welsummers and two different origins would produce alot of different contracts in color specifically what they are breeding for. Too much red in chest are very distracting and not original to the breed what the original breeders are trying to create and it is up to us to maintain the genetic make up of the Welsummer trait itself. An odd chick must be culled out of the breeding stock because you do not want to pollute the genetic pool you are trying to create. 
The egg production are pretty good in some lines while others were NOT made for egg production and focused on the standard itself. Many breeders back then wanted a dual purpose bird that lays a good number of eggs per year AND good table fowl for eating. Some will breed for utility and there ARE breeders out there that would do just focus on one thing. I think egg production is important as well as the good egg color, must be terra cotta, not chocolate or regular brown eggs such like the Barred Rocks.
If you DO get an excellent quality bird that meets almost all the standards (there is never such a perfect bird but try to get as close as you can!) and she does not have good egg production, breed her to a roo that is known for good laying qualities.
With the high feed bills, I daresay that most of us do not profit from selling eggs for hatching, or meat, or egg consumption. People do willing to pay a bit more for darker eggs if they are "favored" for the breed or just the novelty of the color itself or for breeding/raising their own Welsummers from your lines.
Does this help or do I need to clarify more? Let me know and I will do the best I can. The others can chime in.