It's supposed to discourage people from crimes, yes ! But of course, when the cell is composed of 3 cells with laptop, sport equipment, bed and LCD TV with videogames, I have troubles to see how it is supposed to discourage someone.
Also, you keep telling me about death penalty, but I don't remember saying it was a good thing. Actually, I'm against it. Tell me, if prisons aren't a punishment, what prevents people from making crimes ?
As for your last question, no, it won't prevent murders, but you're missing the point here: How are you supposed to prevent crimes when detention conditions are better than what some people have every days ? going by your logic: Giving him a bigger cell won't prevent murders, right ? Giving him top notch meals each day neither right ? What about allowing him to have a girlfriend visiting him every day ? Also, I'm sure that giving him a swimming pool won't prevent murders right ?
The point isn't that giving him a video game or not will prevent murders. The point is that this guy made something terrible, and he's supposed to feel bad about this. But he is also supposed to be punished for what he has done. Prison is a punishment. But not when you're giving people luxury life. Because YES, in a lot of countries, those things could be seen as luxury.