There are too many White people in England and America.
...
They're all in their own home land, and if anything I would expect Nords to greatly out number any other race, considering Nords are built for Skyrim's terrain and weather, and the same is for the other races.
I find it interesting that you would think that America is White people's land. 200+ years ago it was the American Natives land. During that time white man disease and guns killed off so many that we can now call it white man's land.
Add to that the fact that Skyrim takes place 200+ years after OB. Factor in the major global events that occurred during that time. Now look at Morrowind. Is it now (during Skyrim's time) the land of the Dunmer, or the Argonians?
I guess 200 years could make a lot of difference in a countries population. I just listed 2 examples here, one real and one fictional. I suppose given this that Skyrim's population could be rather mixed, though it would still be considered the land of the Nords.