Actually Boroda, the Emperor never mentions the Soviets as a reason for Japan's surrender.
If we have someone who can read Japanese, they can verify the translation from this page at Wikipedia. Copies of the speech are shown there in the original Japanese text.
http://en.wikipedia.org/wiki/Gyokuon-h%C5%8Ds%C5%8DAn English translation of the Emperor's surrender speech that was broadcast over radio to Japan.
http://en.wikisource.org/wiki/Imperial_Rescript_on_SurrenderTO MY GOOD AND LOYAL SUBJECTS:
After deeply pondering the general trends of the world and the current conditions of our Empire, I intend to effect a conclusion to the present situation by resorting to an extraordinary measure.
My subjects, I have ordered the Imperial Government to inform the four Governments of the United States, Great Britain, China and the Soviet Union that our Empire is willing to accept the provisions of their Joint Declaration.
The striving for peace and well-being of our imperial subjects, and the sharing of common happiness and prosperity amongst tens of thousands of nations is the duty left by our Imperial Ancestors, and I am the one who has not forgotten about this duty.
The Empire declared war against the United States and Great Britain for the desire to preserve, by ourselves, the Empire's existence in East Asia and for the region's stability. As to the infringement of other nation's sovereignty and invasion of other territorial entities, those were not my original intent.
By now, the fighting has lasted for nearly four years. Despite the gallantry of our naval and land military forces, the diligence and assiduity of hundreds of civil service officers, and the public devotion and service of one hundred million of our people, the situation in the war has not turned for the better, and the general trends of the world are not advantageous to us either.
In addition, the enemy has recently used a most cruel explosive. The frequent killing of innocents and the effect of destitution it entails are incalculable. Should we continue fighting in the war, it would cause not only the complete Annihilation of our nation, but also the destruction of the human civilization. With this in mind, how should I save billions of our subjects and their posterity, and atone ourselves before the hallowed spirits of Our Imperial Ancestors? This is the reason why I ordered the Imperial Government to accept the Joint Declaration.
I, from the start, have worked with our various Allied nations towards the liberation of East Asia, and I cannot refrain from expressing my deepest sense of regret to our Allies. The thought of our Imperial subjects dying in the battlefields, sacrificing themselves in the line of duty, and those who died in vain and their relatives, pains my heart and body to the point of fragmentation.
As for the bearing of the wounds of war, the tragedies of war, and the welfare of the those who lost their families and careers, it is the objects of our profound solicitude. From today hereafter, the Empire will endure excruciating hardships. I am keenly aware of the feelings of my subjects, but in accordance to the dictates of fate, I am willing to endure the unendurable, tolerate the intolerable, for peace to last thousands of generations.
Having always protected the Imperial State in general, I rely on the loyal subject's integrity and sincerity, and I shall always be with you subjects.
If we become stimulated by sensations, and begin to engender needless complications, engage in fraternal contention and strike or create confusion, we will become astray and lose the confidence of the world. We must rally the nation, and continue from generation to generation to entrench the imperishability of this sacred state.
Aware of the heavy responsibility and the long road ahead, we must focus completely on the future's construction, follow strictly the ways of our noble morals with determination and resolution. We swear to foster and spread the glory and essence of our Imperial State, so we will not fall behind the evolution of the world. It is my hope that my subjects will understand my intentions.