Okay. Let's try and find a way to make this about the character, then.
Alright, say we've got a player who wants to blind his opponent.
If he's a spellcaster, he either knows a spell that does this (possibly with a saving throw involved), or he doesn't. He either has that spell ready or he doesn't. This is pretty clear in the rules. I can see the appeal of this clarity.
If he's a fighter, under the existing D&D rules, he hasn't got many options (as noted upthread, PF's Dirty Trick maneuver is one approach). He has to ask the DM to make a ruling. While DM rulings like this are a part of the game, I can see where this is sometimes a problem, and rules might need to cover the situation more clearly.
So what's to be done here?
Making up a new rule to cover poking someone in the eye or throwing sand in their face is entirely acceptable in my book. However, poking someone in the eye doesn't require specialized training, like a class-exclusive ability does. Anyone can do that, or at least try and have a realistic chance of success. The wizard could do that if he wanted to. Fighters might have skill that makes them more likely to succeed at blinding someone. However, I don't see that anyone is ever likely to spend a feat or other character resource specifically on doing that; it's too specialized. Most will simply let their general combat skill (BAB or the equivalent) take care of that stuff. Moreover, having character options be that specialized creates spamming and balance problems, as others have noted.
The only reason that similarly specialized and powerful options don't necessarily ruin the game when they're in a spell is because spells have limitations. Casters run out of them. Casters have to choose which ones they learn and memorize.
However, those same limitations can't be applied to fighter
characters. They don't have to learn how to poke someone in the eye. They don't have to prepare an eye poke in the morning in case it becomes useful. They don't lose the ability to poke someone in the eye after they try to do it once.
So the fighter character will never be able to exert control over the game world in the same way a wizard character can, because if a fighter had an ability equivalent to, say, glitterdust, but without the limitations of spell slots, it would be game-breaking.
One solution to this is to forget about the character and instead design the game around the player. The player can blind enemies a certain number of times or under certain circumstances, irrespective of what's happening in the game world. If the player is playing a fighter, he stabs the guy in the eye; if he has a wizard, he unleashes some sort of incantation and the target's eye is destroyed by necromantic energy. One could look at 4e's powers as a sort of mangled attempt to do this.
Another solution, which I prefer, is to design rules for the character, not the player, with the philosophy that the rules of the game correlate directly with the natural laws of the game world, but to simply do a better job of designing those rules. As you are well aware, those limitations on magical abilities often aren't very limiting, and as [MENTION=58416]Johnny3D3D[/MENTION], D&D's spellcasters have a far easier time with their magic than most fantasy fiction or even D&D's flavor text would suggest. So I think those limitations should be increased. As you are also aware, D&D has an extremely abstract approach to combat that doesn't describe actions like trying to blind someone (and excludes many other very basic actions and effects of combat). I think the rules should be fleshed out to allow for more different types of harm to be imposed on a target, and combat actions that allow them to be imposed.
Fix those systemic issues, and the fighter fixes itself, without needing to resort to the metagame route. Of course, the fighter and wizard still aren't the same, but their power in the game and their potential to involve the player in utilizing that power is far more equal.
