I would almost think that the fact that political leaders would create statues in their likeness, and they way they would be presented, is a form of propaganda. For example, if we look at the Aulus Metellus (the Orator), and the stance that he takes. This stance basically signified persuading people to take ones side using persuasive arguments rather than force. By displaying this in this statue and displaying it where people can see it, will influence people to think highly of republican values that the Orator represented.
Similarly, if we look at the Augustus of Primaporta, he is taking a non-aggressive stance like the Orator, making him look like a man of persuasion without forcefulness. Then we have the fact that he is barefooted, to make him look holy. The cupid at his right leg is to represent his godly heritage, being of a lineage that traces back to Venus. I would think that all of these details were to impress the audience that gazed upon it.
Even the sculpture where Commodus is likened with Hercules. This is a way to show that he was of divine likeness and had endless strength. Although the attempt was this, he was still seen as vain.
I think that portraying individuals in a certain way in order to impress or influence the way that people see them is a form of propaganda. And this was seen a lot in Roman art.