Nothing kills a sorcerer faster than a theme. With a decent spread of known spells, a sorcerer can cover most of the bases needed. While a wizard can use items to increase his spells known (via scribing extra spells), and spells per day (via wands and such), a sorcerer can also pick up wands and scrolls to cover spells he doesn't know. But overloading on spells of a certain type compounds the lack of spells known. A sorcerer can do the generalist caster thing.
The main tradeoff is between the wizard's unlimited spells known and the sorcerer's spontaneous casting. It sucks to have so few spells known, especially as cool new spells come out. But it also sucks to have the wrong spells prepared - or just not enough of the right ones. There's a huge difference between having 1 or 2 Greater Dispels prepared and having the 10+ that a high level sorcerer can throw when needed. A wizard can spread himself awfully thin, especially when buffs are taken into account. All the other marginal differences pale in light of that difference. If you want the spontaneous casting, there's really no substitute.
Some people are just going to swear by one class or the other based on that difference.