Though as far as the classes being the same...
Oh, and WarDragon, a bit of a warning. I tend to be long-winded, and write long posts.
For the sake of scrolling down, and so you dont hurt your eyes trying to find the latest updates and such, I try to put all my really long rants/articles/novels into Spoiler Blocks.
Read at your own risk.
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My Wizard VS. Sorcerer thoughts, from a numbers stand point.
Early game, power-advantage goes to the wizard with high stats and/or the wizard who is a better planner. He knows more spells, but can't use as many. Unless ambushed, the wizard can prepare for near anything, so the wizard has more tactical sway, but the sorcerer has to use the few spells he has to do everything, or else buy a crossbow.
Mid-game, The game goes to the sorcerer. He has more spells per day than even a specialist wizard, and while he has one or two less feats, and a less adaptable list of spells, unless the sorcerer has chosen a very narrow area of specialty, he or she generally has a spell that will apply in the situation. No cone of cold vs fire giants? Ice storm isn't bad. Warlord threatening you? Charm him, and get away. The wizard may have the advantage of choosing a spells each day that fit exactly what they need, but they are not innately stronger or weaker than the sorcerer unless played tactically better.
High-Game, the wizard can adapt to any situation. Need a spell to defeat a foe? Wish for a scroll of it, cast the spell or scribe it for later use. He can cast any divination spell he wants to get any information he can, and has quite a few more feats than the sorcerer. The sorcerer on the other hand, has a pretty solid list of spells to work with by now (15th-20th level) and their spontaneous casting means if they happen to need 50 fly spells to buypass 50 chasms with long halls in between, they can. Need to teleport between rooms in a dungeon? A sorc with Clairvoyance and Teleport can do it as many as 10 times a day. A wizard, even a prepared one, could do it only 4-6 times before sacrificing the Option to cast other, more powerful spells.
Early Game - Sorc: Narrow list, must make spells work. Wiz: Larger list, can adapt if given preparation.
Mid Game - Sorc: Basic list, can adapt to fit most problems. Wiz: Huge list of options, but can't adapt if a poor choice is made in spell preparation. (What no fireballs? Well, looks like the sorc with his 20+ Scorching Rays will kill the Frost Giants!)
High Game - Sorc: Large list of options, can repeatedly use abilitys without sacrificing adaptibility. Wiz: All options, large list available, still hindered by poor spell choices as usual. (Do I prepare 4 Polar Rays because I know a Red Dragon was the one who made the deal with the Frost Giants, or do I ready myself to deal with the giants who are more numerous...)
Both classes do the same thing: Cast Arcane spells. Wizards 1-20 start out with more advantages, but in the end, sorcerers get a bigger benifit in the long run.
Now, we all know this. But as both classes keep progressing to infinity, the sorcerer continues to gain spells known through bonus feats (at the cost of power) which have become numerous. And lets face it, knowing every spell won't help you against a demi-lich, who is only vulnerable to really one spell. (Shatter)
Eventually both classes through bonus feats will know every useful spell, but assuming the sats are the same, the sorcerer has a much bigger choice in the options available to him. Potentally every option if fresh for the day. A wizard will only have a small fraction of his repotoire at his command. You have a Billion spells in your book? Well, you don't have nearly the spellslots to prepare them all.
At super high epic levels, (somewhere between level 50 and 1000) it seems the roles reverse.

Wizard becomes a very strong class with a narrow list of options, while the sorcerer gains power much more slowly, but have infinitly more options at any moment.
Picture a line graph, depicting the rate of growth of each class in several areas. In the are of "options" the sorcerer starts off low on options and flexibility, but the line has a quadratic curve to it, sharply increasing in power to near infinity as time progresses. The wizard starts off with a large ammount of options, and gains them quite quickly, but the wizards "options" growth rate is less.
Sure the wizard can easily get every spell. Heck, scribing every spell in the PHB costs about 300k in gold. (Though a Blessed Book filled with every spell is only about 40k...) But once the wizard has every spell, he doesnt always have them all prepared.
And even if he or she did, even if he or she had Fireball, and Lightning Bolt, and Haste, and Confusion, when he runs into the Flaming, Incorporeal Undead, He or she only has one Lightning Bolt to bring against it. The sorcerer, can turn all his or her (3rd to 9th) spell slots (up to 36 of em before bonus spells) into as many lightning bolts as needed, and still has all of his or her other options.
The reason (I have deduced) to merging the 2 classes is because eventually they both use the same spells. (Scorching Ray is mathematically strong) And once you get Alter Reality, preparing spells become useless anyway, because it is wish on steroids. And if your spellcasting stat keeps going up, both classes have about the same number of spells per day. If the difference of about 10-20 spells, does it matter what class you are when your primary stat, lets say 810, gives +100 first level spells... and +98 ninth level?[/sblock]