It's just that... in past DMCs, it was hard to actually see a proper conversation in the games. Dante only said one liners left and right, Vergil never talked, and the bad guy went off on a limb about how he wanted to rule the world and kill people and stuff.
They make this Vergil talk as much as they are making the new Dante talk. It's just a way to give more realism to the game. I gotta say, compared to the original, I don't like what we have been shown of this Vergil very much because (while there are some instances of doubt about his character) they are literally making him look more of a wimp who would not do something if you were to talk back to him. Is that his real character? I'm willing to bet that it isn't, but hey... some people might take it too seriously.