Something that a GM needs to remember when designing foes for the players - especially foes created using the same rules the players use (humanoid enemies with class levels), is the difference in role between a PC and an enemy.
A PC sticks around. He faces, (in theory) on average, four encounters a day, every day. Generally, the player who makes him is planning on playing him for the duration of the campaign. The PC is created with the intent to live.
An enemy doesn't last all that long. One direct encounter and he's gone. Caput. So long, sirs, and thanks for all the fish. An enemy is created with the intent to die. He's supposed to challenge the PCs, push them hard, but in the end, if all goes according to plan, he should be laying down and they should be standing up.
This doesn't mean that PCs should never die, or that an enemy should never live to fight another day. If a player does something dumb and doesn't find his way out of it, the PC dies. If the player hits an inexplicable string of bad luck, the PC dies. If the enemy is planned to be a recurring villain and the players don't thwart his escape plan, the enemy lives.
However, in general, the plan is that the players win - and live - and the enemy loses. The penalty for his loss is death.
Which brings us to the topic of this little bit of writing. Since PCs and enemies have different roles, it makes sense that they'd use different effects. This is especially true of mages.
In the hands of a PC, a nuke spell is a subpar piece of magic (usually). In D&D, a foe with 1 HP is just as dangerous as a foe with 1000 HP. Thus, damaging a bunch of enemies but not enough to kill them (which is what nukes do against balanced foes) is generally inferior to killing a single foe with a removal spell.
However, in the hands of an opposing mage, a nuke is terrifying. When you're on the second encounter of the day, and you know there's two more left to get through on your current stock of hit points and the priest's current stock of spells, a fireball is one of the last things you want to see heading your way. No, it won't kill you... but it'll hurt you and your friends enough to force you to be even more careful the rest of the day.
A fireball is a great tool of drama in the hands of a GM, but a lousy tactical tool for a player character. However, those death spells that the PC mages are lobbing around are bad in the hands of a GM. The moment of tension they create isn't worth the frustration of losing a character to a single bad roll.
Of course, when a player's agreed to have their character drop for drama's sake, all bets are off. ;-)