Here is what I could dig up, this doesn't really prove anything, but may help with the why they explained it that way. If I'm reading this right, it seems that the common thread is that the powers of the statue all were influenced in some way by Babylonian religion/tradition. The other aspect to keep in mind, is the king of the north, and king of the south (Dan chapter 11). In there are pieces of data that are supposed to identify these powers of the statue.
Asian powers.
What was the First World Power? Was it Babylon? No, although Nimrod did set up Babylon and there gave a start to what became the world empire of false religion. God’s action prevented it from becoming the first political world power. (Gen. 10:8-10; 11:8, 9) The Babylonish religious empire reigned over or sat on top of the first symbolic mountain, the Egyptian World Power, the first political world power of Bible history. The second was Assyria; the third, Babylon, which, while being religious, also became at this time the dominant political world power; the fourth, Medo-Persia; the fifth, ancient Greece or Macedonia; the sixth, Rome; the seventh, Britain and America, a combination or dual world power. All these world powers were very strongly influenced by religion, which was Babylonish religion [Asian powers did not fit this criteria], so that as a religious empire Babylon the Great of the Bible ruled all along. She did not pass away when the ancient city of Babylon fell in 539 B.C.E. to the Fourth World Power of Medo-Persia, nor when that city finally perished during the time of the Roman World Power. Babylon the Great survives to this day as a religious empire. (w67 3/1 p 155)
Spain/France.
By the year 1763 the British Empire had defeated Spain and France, both of which were powerful sections of the Holy Roman Empire. From then on, the British Empire demonstrated herself to be the mistress of the seas and the Seventh World Power of Bible prophecy. Even after the thirteen American colonies broke away to establish the United States of America, the British Empire grew to embrace a quarter of the earth’s surface and a quarter of its population. The Seventh World Power gained still greater power when the United States of America collaborated with Britain to form the Anglo-American Dual World Power. Economically and militarily it was indeed a “king fierce in countenance. (w71 12/1 p.717)