I just came across this post from 2002 while reading more about Norwegian and Minnesota Whist. I do not have specific answers regarding your questions, but I do have some interesting insight.
I grew up in Minnesota with family from North Dakota. Whist was the favorite card game of my grandmother, so we often played it at family get-togethers. I was unaware that this game was called anything other than "Whist" until reading about Whist online tonight. I now know that we always played Norwegian/Minnesota Whist.
I now live in Denmark, where the version of Whist that I grew up playing is also played. I also Google searched for the game "Norwegian Whist" and "Danish Whist" in the Danish language. They are the same game, although it is referred to as "Danish Whist" here in Denmark rather than "Norwegian Whist".
So, with that said, I suppose the Whist played in Minnesota and the surrounding areas really is a tradition passed down from our Scandinavian ancestors.
Happy Scandinavian Whist playing! :)