Kind of another take on the discussion of experience points...
Experience points are the least dissociated mechanic in the book.
Look at ability scores. Strength, Intelligence, etc. refer to things in the game, but what does "1 Strength point" mean? Nothing in the game world, at least in any version of TSR D&D I'm familiar with. In AD&D and Greyhawk supplement, individual points mean nothing; only certain point thresholds change carrying capacity or increase damage. And in the LBBs, there's no correspondence between 1 point of any ability and anything in the game world.
Same with hit dice and hit points. Sure, for monsters, hit dice are a rough guide to the size of the creature, but there's no correspondence between specific size ranges and specific hit dice, and there are several exceptions. It's notably more dissociated when talking about player characters.
I've seen houserules that equate 1 Strength point to 1 stone carrying capacity, or that try to interpret hit points or damage in-game, instead of as some kind of abstraction of luck. But by the book, stripped down to the barest level, they are abstractions.
Not experience points, though. 1 gp = 1 xp. We all know the formula. Experience points, even stripped of the "reputation" interpretation I use, have a literal representation in the game world. Your cumulative experience points are an estimate of your cumulative wealth. A character in the world can't say "I bet that warrior has Strength 15," but the same character could certainly say "I bet that warrior has brought back about 10,000 gold pieces worth of treasure over the years. I think I'll charge him 100 gp in taxes."