This is all very interesting for me...
In a few words, i suppose it all depends on the reason you want the dog for. Generaly,if you want a show dog you don't really care if it can work or not (i'm not saying this is good). If you want to work out you will chose a dog from working lines. It's great if the same dog can win both in shows and work field. Ex: we have a Mal here in Romania who is great in dogshows, won BOB in a big dog show in autumn and in Feb he was first positioned in a sled-contest of speed, at 5 dogs category. (The owners also have a Mal that pulled a car at a TV show here, beating the record in our country, but this one is not show-quality)
I live in a different area in the contry and I don't have so much snow like this ppl, but when we have snow we always go with Carlos and he gets to pull the sled (he can take 2 adults with no effort). And he is a Champ in dogshows. So there are dogs that do both. (guess i'm trying to always see the good part of thinks, me, being optimistic and all
)
And if you read the standard of a Alaskan Mal, it describes the working dog. (one of many reasons I absolutely love this breed is they are dogs that haven't changed much from their assumed beginings)
Hope I didn't disturb anyone, it's just a personal opinion.
I agree there are breeds that cannot fulfill their original purpose anymore, or not properly, at least.