Thasmodious
First Post
1) They still do. A flying wizard is plenty easy to hit, by a challenging foe. That and dimension door just put the wizard on the run, they gain him time. Stoneskin is cool (unless the enemies have adamantine) but it isn't a certain thing against high level opponents that can dish out lots of damage, and you waste your round casting it, so the enemy is already in front of you next round if the fighter isn't there. Summoning a dire bear is a round casting time, so the DC is damage + spell level + 10. At that high level, anything that causes a concentration check can easily do enough damage to make the check near impossible.
2) You can still get hit casting defensively, you just don't provoke an attack of opportunity. Any spell that is a round or more is going to have a difficult concentration check (Damage+10+ spell level). Plus you need to make the initial concentration check for the defensive casting (which is pretty easy).
Wizards are my favorite class (well, tied with fighters, 3e was mixed emotions for me, wizards rocked, fighters sucked). I know them quite well and have played wizards extensively throughout the 3e years. A party and a wizard certainly don't need a fighter. It's nice to have a hit point soak in between you and the foes you are about to obliterate, but it is absolutely not necessary. You don't need to cast fly, you have a cloak of flying. Or boots of levitation at middle levels. Ranged attacks aren't a huge threat as they are generally much weaker than what brutish, bashing monsters can do. Dimension door has a range of a few hundred feet. So do many of my spells. You don't DD where you are still in range of a charge from the frost giant. An animal summons lasts for more than one round as well, so if you really need a pool of points to stand in front of a monster, its well worth it. And you cast it first, not after the monster is eating you. You do have party members, hopefully they like to keep you in the back and clear to do your thing. Protection spells are a backup. Metamagic is your friend. Your job is to not stand in front of beasties and you have tons of tools with which to do just that. Your battlefield control can make safe spots for you. Shut things off with a wall of force then levitate above it, surround enemies with a wall of fire, cloak yourself in fog, throw up some webs, etc.
Even when you have to make a concentration check, its not difficult at high levels. You have plenty of skill points and not much to spend them on, so maxed concentration is standard, plus a bit of Con. Throw in some focus and an item if you need the boost because you are often getting hit a lot (and you really shouldn't be). If you are making regular concentration checks, defensively or otherwise, you're doing it wrong.
That fighters and other straight melee classes lagged well behind casters (from mid levels on up) is not something that is open for debate. It is a problem that's long been mathematically established and acknowledged by the game designers. ToB was an effort to level the playing field a bit, and was quite successful at it, but it came out 7 years into the edition. (this is more in response to insanogeddon than Pain)