It may have felt good, but it seems pretty bizarre. Bob the barbarian can't know whether he likes his friend Will the wizard to cast haste to make him faster or fireball to set him up for a great cleave unless he has spellcraft? And he can't know that the fireball stays the same in area but increases in power as Will gains more skill and experience without knowledge: arcana? Bizarre. Next, I suppose you'll tell me that Filbert the fighter who grew up next to the trollfens in the Duchy of Tenh can't know that trolls regenerate unless he has ranks in the appropriate knowledge skill and can also tell the difference between ogres, hill giants, storm giants, and cloud giants on sight. And Cletis the cleric can't recognize his own holy symbol without a knowledge: religion roll--or, just as bad, Farrel the Pholtan half-orc barbarian can't tell the symbol of Pholtus from a symbol of Iuz without ranks of Knowledge: religion and a successful skill check even though he grew up in the Theocracy of the freaking Pale.
Similarly, any PC wizard who has adventured with or fought a barbarian should know the basics about rage: stronger, tougher, easier to hit, and might well be mortally wounded but not notice until he dies when the adrenalin wears off (usually in 30 seconds to a minute). After the beserker comes out of the rage, he is generally winded for a while. Will the wizard would have to be blind not to notice these effects.
And there's not just direct experience to consider. Any PC who's more than first or second level should have a general idea of what spells the cleric might cast on him in combat--if not from direct experience, because when he was sitting around with the other caravan guards in Jaramai Twist's caravan, he heard Patrick the Paladin saying things like "Yeah, he was twelve feet tall and had a club the size of a tree trunk, but I wasn't afraid for Cleo the cleric had blessed my armor and shield that morning with the power of Heironeous making it as hard as enchanted metal and had invoked a miracle that he would bear some of my wounds, and when we saw the great beast, he called upon the Invincible Knight to shield me through his faith. So I strode forward and smote the monster with the power of Heironeous." If Bob the barbarian can talk with Patrick the Paladin about his experiences and never get any idea that clerics like Cleo can cast Magic Vestment, Shield Other, and Shield of Fatih, then either Patrick is keeping his party's winning battle tactics very close to his chest and exaggerating his own role to make himself seem more heroic or Bob is deaf.
Similarly, if Bob the barbarian ever walks into a temple of Heironeous and asks to buy healing potions because he's going to fight the demons in Almor, you can bet that the priest of paladin there is likely to say something like: "Fighting the demons you say? With that sword? I think not. Son, even the weakest of the true demons shrug off normal weapons. To penetrate their resistance, you should bear a weapon forged of cold iron. But I see you are not the type to fight only the weakest of demons. For moderately powerful fiends, you will need a blessed weapon if you wish to injure them. Fortunately, we sell an oil here which will provide just such a blessing. If you see a demon--you know vaguely anthropomorphic thing with bat wings calling down blasphemies--apply it to your weapon that you may strike true."
Since he visited the Temple of Kord before his previous adventure, Bob replies, "But at the temple of Kord they told me that silver was good for devils...now you say cold iron is good for demons, how do I know the difference?"
To that, the wise priest replies, "That is a subject worthy of study by holy champions and men not easily corrupted. Ask Cleo the Cleric who travels with you... or, better yet, buy this oil of bless weapon for it will enable you to smite both demons and devils. At only 100gp, it's a steal."
Bob the barbarian thinks (honest, he really does) back to the last time he asked Will the wizard why his sword wasn't so effective against the disgusting bag of putresence summoned by the priest of Hextor at the siege of Mowbrenn. "But, I think Will said that some creatures need only silver, some cold iron, some holy weapons, and some both. How does this oil solve all my problems again?"
"Ahhh," says the priest. "Do not let the erudition of your friends confuse you. What he said is true, but blessing weapons like this oil enables you to smite both demons and devils of all but the greatest power. If you ordinarily use a cold iron sword, you will still strike true against the most powerful demons, but let's be honest, should you encounter one of those, no sword will help you, nor will it help you against the most powerful of devils. Such fiends are only for the greatest of champions to face. If anything you do can make a difference, this oil will suffice for your needs. And, if you run into such a fiend as this oil does not help against, pray to Heironeous for your life and flee for it is not courage to but foolishness for you to stand against such a foe."
Does listening to the priest's well intentioned sales pitch give him a rank of Knowledge: planes. Heck no. But it does give him all he needs to know to defeat the DR of all but the most powerful demons and devils.
D&D characters inevitably learn a lot about their world that is not represented by knowledge ranks. Insisting that players play their characters like blank slates (or, to tell the truth, even worse, since there's always a chance a character might randomly pick the best option) is not insisting on role-playing. It's just a more self-righteous version of meta-gaming that was previously termed "anti-"metagaming.