The bomb ain't the bomb?

In this article, http://www.boston.com/bostonglobe/ideas/articles/2011/08/07/why_did_japan_surrender/?page=full the Boston Globe explores a historian's theory that the atomic bomb was NOT the decisive reason for Japan's surrender in WWII.

The article suggests that the historian's contention that the real cause was the Soviet declaration of war against Japan days later is more than the evidence supports....but more striking is the claim that many historians agree that the bomb can't be called the main reason either. Further, that the atomic bomb was not a big striking difference in war, but just an incremental change to a country that had already seen many cities firebombed.