JoeGKushner
Adventurer
The funny thing, in in 4e, I totally 'gork' this type of experience.
Yeah - as mentioned, "doing damage" is usually a suboptimal choice for 3.X wizards.* Rather than a spell which removes, say, a quarter to a half of an enemy's hit points (like a MM against a low-level target), it is far, far better to completely shut that enemy down: Sleep, Color Spray, Grease, etc.
In a game where the action economy is so important, removing a significant portion of your enemies' actions tends to almost always be a stronger choice. For example, in a standard dungeon room fight, it is far better to put a wall (even a temporary one) in between half of the opponents and your party than it is to fireball the majority of bad guys (or, alternatively, put half of them to sleep). This essentially uses one spell to create two mini-encounters, and if the entire encounter was designed to be a balanced challenge, each individual mini-encounter will be a cakewalk.
Also, this isn't really limited to wizards - clerics and druids are also just as much benefactors of the "magic makes me hard to kill" rules; they just don't start out with Scribe Scroll or get bonus item creation feats as they advance.
* See also my Pathfinder Magus playtest notes in the PF forum, wherein I rather quickly sub out my Burning Hands spell for another Shield and my Ray of Frost for Daze.