I have similar thoughts. Huge mass of land, hard to civilize if you keep migrating from place to place for food, shelter. Different rate of births possibly due to culture. Also no slavery, it seems sometimes man doesn't civilize if its not at someone else's cost.
However, the Bering Land Bridge is a rough theory to agree with. http://en.wikipedia.org/wiki/Bering_land_bridge
10,000 to 20,000 years ago?
Maybe those canoes are built better than we thought :)
Naw, I just think they have the years wrong. Have you ever seen a picture of the berring strait? I saw one in a history book once that showed how much water there is covering it. You don't need an ice age to freeze that, I always thought globing warming and just weather shifts account for the fact that it's now under water.