Romans continued the Greek’s perfection of the human form, but in an odd way.
They would carve their sculptures with winkles, frowns, warts, and try to stay as true to their subject as much as possible. I think this is due in part to the Roman’s need for individuality, especially in political situations. You can think of the Roman busts as advertisements of the leaders’ reigns.
I believe they wanted to take steps away from the Greek past while still using Greek knowledge. There was less focus on super human attributes and beauty (though the emperors still likened themselves as to gods in the way they portrayed themselves with battle motifs).
However, this was all done with a weird sense of duality. Sometimes they would carve themselves with flaws, but not show themselves as growing old. They even portrayed themselves as looking like previous leaders to whom they had no relation.
With their paintings, you can tell that they wanted to capture verism there, too. Still-lifes were painted; attempts to correctly simulate glass were tried (and not wholly failed).
All in all, I believe these veristic tendencies were motivated by some form of individuality. When you saw a sculpture, they wanted you to think, “This is what my leader looks like, not necessarily a god, but a great man.”