The Roman's idea of showing every blemish, no matter how big or small, seems to be less about art and more about achieving a true portrayal of the person being depicted. But why? If you go back a few years to the Egyptians, they were obsessed with immortality and even used their art, in some cases, as a means for housing their souls in the afterlife. Fast forward a couple of years and the Greeks began creating sculpture influenced by the Egyptians. Their sculpture was not for the purpose of eternal life, as far as we know, but for honoring the beauty of the body. As time went on and their sculpture progressed it became more portrait like, but not entirely. A sculpture of an individual could still be confused with another person which looked similar (unless of course, you're talking about “Conehead” Pericles).
That brings us back to the Romans who were in love with Greek sculpture. It could be said that they took their ideas about sculpture a little further in the realism department. But verism...why the warts and all? I think it has to do with the honoring of the individual. A patrician who thought very highly of himself would want to be remembered forever, and a bust that did not display the unique features of the individual might be confused with any random citizen and not the important leader from the wealthy background.
In the portrait of a Roman general from the Sanctuary of Hercules the traditional veristic style is used in the man's face, but the body is that of a young man. It is possible that the Romans held a direct correlation between age and wisdom. Perhaps the patricians were pushing “respect your elders” propaganda.