A bit OTT, you can't say that because someone played CS that its the reason why he went on a rampage. Surely the reason is the extremely lax gun control laws in the USA, coupled with someone who was known to be mentally unstable.
I do however think that GTA is getting a bit too much now, and that it should be restricted to adults. The problem there is adults will buy the game for kids without thinking so its not fool proof.
I know the difference between a game and real life, and all of you most likely do too. Its just that a small minority who play the game obessively (who plays GTA for 15 hours a day?!?!?!?! Insane!) who may go on to commit crimes. But then again its a childish repsone to the "why did you do it?" quesiton "GTAIV made me do it sir!". Thats like me getting stopped for speeding and saying "the go faster stripes made me do it officer!"