According to this Danish site, http://www.nenne.com/nordicway/index.html
It seems the spelling is a regional thing... perhaps it's an Anglicization, I don't know, though it doesn't appear so...
Why don't you ask one?
quote:
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So when we today speak of asatro, asatru or Norse Paganism, we must be careful not to misunderstand each other--this because there are all different kinds of people who call themselves "Asatruars"--not even mentioning all New-Agers and suchlike that desecrate and abuse the Way by stealing and misusing sacred signs and practices in the same, most sacrilegious, way that they expropriate traditions and desecrate objects, places and symbols that are sacred to, say, native Americans.
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First there are those who confess to and pay hommage to the Norse Gods--period--who leave out the "rest". By this I mean that they seem to have little or no place in their world for the other parts of "the Ancient Way"--the popular faith, traditions and culture as well as moral, customs, the spirits of the land and all those other beings and creatures that I cannot start to mention, mainly because there are no words for them in the English language. Many of these people you'll find outside of Scandinavia or the Nordic countries. They might live in the United States or Australia, but you might also find these people in the bigger towns and cities of Scandinavia. They therefore have little or no contact with said spirits of the land, the non-Scandinavians among them also, naturally, lack the natural connection to the "Ways" and popular faith of the Scandinavian people that have "survived" christianity. These people often define "Asatru" or ("Asatro" if they're Scandinavians) as a reconstruction of the faith in the Old Gods which, of course, is exactly what it is all about -- as far as asatru goes...
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Finally, there are those who follow the "Nordic Way" or the "Ancient Way" . Confusingly, these people might also refer to themselves as "Asatruars" (or "Asatroende" in Scandinavia) "Pagans" or "Heathens", but have a different approach to life and the world they live in than do the others I mentioned earlier. You could say that both "Asatru" and "The Nordic Way" are founded upon the same basic values--tolerance, honesty, loyalty, reverence for nature and all life. Using the name Asatru or Asatro when speaking of the Way is however misleading, because the faith is not restricted to the Aesir Gods alone. There are other gods in Norse mythology and folk religion as well, there are the spirits of the land, there is the culture and the customs--the Way of the Nordic people. In recent times confessional societies have been formed in the Nordic countries, open to those who wish to restore the Ancient Way, reclaim their cultural heritage and honour the ways of the old Gods. You might recognize these confessional societies by name (with a few exceptions they're called something containing the word "Sed" or "Sidr"--meaning "The Way").
It seems the spelling is a regional thing... perhaps it's an Anglicization, I don't know, though it doesn't appear so...
Why don't you ask one?