The only thing close to real-world violence I have ever encountered involving video games, has been over frustration in playing them... And having titles I want to play canceled, but that still did not lead to me shooting anyone.
Really? Just because GTAIV was being played by someone who should not even be playing the game for another 10 years (And keep in mind, we do not actually know yet if the kid in question was even playing just before this happened.), it is immidiately assumed it was done "on purpose" because of the game? Are you freaking kidding me?