In the World of Warcraft, the cost of dying is really pretty minimal. Yes, there's the trouble of running from the graveyard to your corpse and yes you take 10% durability damage to all of your equipped gear (the cost goes up to 25% if you need to spirit rez). So you lose a minute or two of time running back to your corpse eating/drinking/bandaging, and rebuffing yourself before getting right back to where you left off. In terms of gameplay, you're not really set back at all -- you don't lose experience or levels from death. And sometimes death can even be beneficial to your character: say, by killing one of a pack of three monsters (dying in the process), and then coming back to take out the second and the third. You've just managed to kill a group of monsters larger than you could have killed alone -- all by benefit of the death system!
But the penalty for death is so light that there's not really much reason to avoid it. Oh, I know the time spent in corpse runs adds up and the cost of repairing gear only gets higher and higher. But it's not the end of the world if you die -- and it's hardly even the end of your online character. And so there are some players who think the death penalty needs to be harsher. If death mattered, we'd all be playing more cautiously -- in fact, the difference in playstyle would make it a whole new game. But it would make the most difference in the raiding game -- I can't say I've ever learned an encounter without a few deaths. Losing experience or levels for wiping in a raid situation?
"Sorry everyone, I just leveled down to 69 from that wipe, have to go grind."