The wizard (or burst/blast player) isn't immune to blind - he simply doesn't have as much trouble as most hitting. He still gives Combat Advantage, has his options dropped to exclude Ranged or take -5, and still can't flank.
He targets the enemy in the exact same way as every other player - he just has a lot of "granande" options. Last time I checked a granade didn't need to see you to hit you (rather important as a grande has no eyes - or ears or any other sensory abilities).
If his friends can shout "Ten O Clock - 30 ft" or he hears the person's feet slapping the ground as they move he throws his "granade" in the right area more or less - and the explosion then doesn't give a damn if the person in its blast-radius is seeable or not they just get smacked in the face with a shockwave and are effected or not based on the strength of their AC/NAD.
Burst/blast users are impeded in targetting the same as any player - the blast or burst is not impeded in hitting if it was targetted well enough. This is why blast/burst are not effectted by invis/blind.
And if you then look at the logic of non-explosion Burst/Blast powers you can follow the same logic. A fighter hitting everyone around him just sweeps his sword in a circle and impacts on people or not (swinging high to avoid his allies as they go "Not me you idiot!" and he recognises their voice so swings wide, or they recoginse what he is about to do, having seen him do it before, and take evasive action), the ranger shooting everyone in a burst just loads and fires at every spot he can and if he hits something or not depends on the target.
Bursts/Blasts are effectted by targeting issues (where to put the area you intend to target) not by aiming issues against individual targets. Thus they don't get effectted by the concealment issues - makes pretty good sense to me.
As I see it your objection against Area abilities being uneffected is the same as your general objection. You don't like "Blindness" allowing you to find a person's square easily - if this was not true then targeting Area abilities would be just like knowing where to throw a granade and then letting the grande work out who it hit without issue. I understand that blindness in real life would be more damaging than it is in 4E, but then so would immobolised, or helpless or any other effect if you imposed it in the correct manner - 'Blind' is just a word used to impose some penalties not necessarily the exactly accurate IRL term for the exact in-game effect.
I am often 'blinded' by sunlight - I can still see, but I have blobs of colour in the middle of my vision and can't focus very well. I think you would have less trouble if you redifined 'Blind' as 'Vision Impared' and 'Invisable' as 'Well Camoflauged/Translusent'.