Isn't it also true that in Scandinavia religion started losing ground earlier and faster than in the rest of the West? As far as I know, religion is barely relevant for most scandinavians (apart from the influence it has had on all western culture, of course), whereas it still greatly influences the worldview of most americans.

May be protestantism is the origin of this kind of work ethics, probably exacerbated by american history (colonising a new world, carving a new place for themselves in a barely-known land...).