I think it's important that the paladin get experience for the traps.
It's been said before but the logic bears repeating:
Situation 1: The party survived. The rogue moves down the corridoor taking 10 on search. He finds the traps. He takes 10 on disable device. He disarms the traps. The party gains experience for the rogue using his class abilities to avoid sustaining harm from the traps.
Situation 2: The rest of the party survived--but barely. The rogue moves along the coridoor taking 10 on search. He finds the traps but realizes that he can't disable them (b/c he has very few ranks in disable device and they're magic traps). The wizard has Foresight up and says that they're fear traps. So the paladin moves forward and sets them off. The party should gain xp for creatively disabling the traps.
Situation 3: There's no paladin in the party but the cleric with his protection domain used protective ward on the CG fighter before his death. The CG fighter survived. He walks down the corridoor, takes no damage from Holy Smite (although the LN cleric would've if he'd survived), makes his save against contagion (due to the protective ward), and runs like a little girl when cause fear hits him. . . but it only lasts one round (lucky roll) and he's heavily encumbered with the bodies of his companions so he only moves 10 feet. Then the fear wears off and he escapes. I suspect he gains experience too.
Situation 4: It's the NN fighter/rogue (archer) with a hideously high reflex save who survives. He makes his reflex save and evades the Holy Smite. The next traps are both fireball traps. He evades them too. I suspect he gets experience despite having used his class abilities to avoid the effects of the traps.
Situation 5: A group of four paladins encounters some Vargoiles. They fight them and defeat them. They encounter a shadow mastiff. They fight it and defeat it. (Being immune to fear helps a lot against such creatures). Do they get less xp than a group of four fighter/barbarians who won the same encounters? No. The paladins are immune to the creatures' special abilities but the fighter/barbarians can rage, have more hit points, and a whole lot more feats which make the fighting part easier for them to overcome.
Situation 6: A LN weapon master challenges a member of the party to single combat. Would a fighter get more experience than a paladin? Of course not. But the fighter's class abilities (his feats) will make him able to disarm or sunder the weapon master's weapon and will let him do more damage to the weapon master (weapon specialization), etc. The paladin faces significantly more risk from the combat than the fighter does.
Situation 7: The final encounter with the BBEG is set up to be a very challenging fight. He's six levels higher than the party and has two tough henchmen. Unfortunately, the fighter/barbarian with his war scythe wins initiative. He rages and, with an amazing string of luck, he rolls a natural 20 and confirms, killing the BBEG outright with a 200 point smackdown--he then uses Great Cleave and that incredible string of luck to kill both of the henchmen rolling natural 20s on them too (I've had a character get that lucky once--but it was in the warmup encounter where it didn't matter). Despite the fact that the party took no damage at all, they should gain full XP. (After all, the bad guy could've rolled nat 20's on the good guys instead--would they get more xp for that?)
What I think these situations demonstrate is that xp is only loosely corresponded to risk. (If XP corresponds to risk, it corresponds to the risk faced by a theoretical average adventurer of the party's level that is immune to nothing and doesn't have lucky or unlucky streaks with his dice). If a character's class ability renders them immune to a situation that would otherwise be risky, they get xp. If a character uses his wits and averts risk, he gets XP. If a character is clever and defeats the risk, he gets XP.
The paladin (unwittingly) used his class abilities to defeat the traps, therefore he should get XP. If he'd had different class abilities (like weapon specialization, for instance), other encounters might have been easier but he had paladin class abilities so other encounters were harder and the traps were easier. He shouldn't be penalized for that.
