D&D 4th Edition makes death rare. A
Character death is a big driving force for players, and provides the primary dramatic tension. Death is always scary. For a long time, the possible death of your character (usually via poor Hit Point rolls and good monster Hit Dice rolls) created a lot of the tension in D&D–will the next monster murder my character? Will this boss crush her?
Now that 4E makes death rare, combat is less of a risk than before, and death is no longer a driving force. That means that DMs must now make the overall story more interesting.
The story itself must be dramatically interesting now. DMs can’t rely on possible death for drama.
I wonder if 4E’s designers intended this, or if it was a lucky result of incorporating player feedback that random character death in the middle of a dungeon isn’t fun.