I mentioned in my little rant about experience yesterday that there were two early inclusions or changes to the rules that muddied the waters of experience, luring some people into thinking of "experience" as representing actual learning instead of something else. My claim is that, originally, "experience" was meant to be more meta, just a way to allow active characters to change over time. If you are going to make it represent something more concrete in the game world, I would equate it to the confidence and reputation gained from bragging about your experiences and returning from adventures with fabulous wealth. After all, obtaining wealth or slaying monsters through trickery, bypassing the risk, doesn't reduce the XP award.
But in the original rules, Gary did add a provision that took risk into account: if you are a higher level than the monster guarding a treasure, both the experience from slaying the monster and the experience from retrieving the treasure are reduced. Less risk, less experience, but only in that case; there's no hint of awarding half experience for stealing a treasure instead of fighting for it, for example.
And in the Greyhawk supplement, Gary changed the experience rules for slain monsters, making special abilities matter. Previously, there was no difference between fighting an ogre and fighting a 4 HD poisonous, fire-breathing beast; you earned the same experience, regardless of the difference in risk. The new experience table awards a bonus for monsters with poison and fire-breathing, over and above the experience based on hit dice. There's still no adjustment for the risk in retrieving treasure: you get the same experience from 100 gold coins regardless of whether it was guarded by a monster, a trap, or nothing at all.
Both these rules make it seem like risk should matter, and started a discussion about what actions should earn experience. For example, there was a general consensus that you shouldn't earn experience for earning wages or trading goods at a profit. This lead to a debate about whether a wizard should get experience for making magic items, especially if the items are sold. Some other systems added experience for casting spells -- but only in combat; you wouldn't want some magic-user casting Light all day going up a level.
I already abstain from the Greyhawk XP awards, but now I think I should drop adjustments for differences in level, except in extreme cases. Sure, a mighty champion who returns to town bragging about wrestling a bunny shouldn't get much experience, but otherwise, risk shouldn't matter.