For the purposes of answering my question, probably the most relevant point is 4 along with his statement as to why Elihu was sent. Wikipedia notes and agrees with these points and adds this: "The speeches of Elihu contradict the fundamental opinions expressed by the 'friendly accusers' in the central body of the text, that it is impossible that the righteous should suffer, all pain being a punishment for some sin. Elihu states that suffering may be decreed for the righteous as a protection against greater sin, for moral betterment and warning, and to elicit greater trust and dependence on a merciful, compassionate God in the midst of adversity."
So now we can see that there is, in fact, at least one difference in Elihu's speech. He points out a positive reason why Job is suffering instead of blatantly accusing him of some hidden sin. But what about Stedman's option number 4 in which Elihu claims to speak from revelation? He does indeed claim this in Job 36:2 - Bear with me a little, and I will show you, for I have yet something to say on God's behalf. So was God not angry with Elihu because Elihu was carrying a message from Yahweh himself? It's possible.
Whether you agree with the opinions of those whom I researched, or you agree with the thoughts of the ESV Bible, they both seem to agree on at least one point, that Elihu prepared Job for the whirlwind speech.
So why didn't God include him in the chastisement? I like the idea that Yahweh sent Elihu to answer Job's cry for an explanation of his suffering and that God sent that message through Elihu. God was angered with Eliphaz, Bildad, and Zophar because of their false accusations against Job; but Elihu relayed Yahweh's message to Job and prepared Job for God's speech.
I have personally come to the conclusion that, basically, Elihu was used by Yahweh, and that's why he didn't include Elihu in his scolding.