I couldn't even watch more than a minute of that video because it was so ridiculous. The only thing I would say is true is that violence in general is exposed more these days and that may have some kind of effect on young people. Mainly it would desensitize them to violence, but a violent video game would only play a small part in that. Movies are more violent these days and they actually depict people getting hurt not polygons and pixels.
The guy who did the VA massacre was revealed as was some of his mental state which was described as "troubled." It sounds like he considered the world his enemy and I doubt he got the idea to go on a rampage from playing GTA(if he even did ever play it). He was described as a loner and quiet and I doubt that type of guy was in his dorm room yelling, "Yeah, die bastard" while playing GTA. In fact he was an English major and it was revealed that many of his writings in class were disturbing and actually noted by teachers.
So increased exposure to violent video games is not good but it's hardly the cause for this incident. There may have been someone who had the idea to do such a thing from playing GTA, but I've heard of someone doing violent things because he said the world around him was the Matrix. If you get that trapped in fiction to the point of hurting someone I think it's more an issue of mental state. A person like that could have read a Stephen King book and done something crazy. What would we do then, ban all his books.