My son has ADHD, and you'd be surprised. There IS some sort of physical problem, and they are using drugs to compensate. One of the "Interesting" tests they did on my son when he was like 3-4 years old. Get a large sheet of paper, and put it up on an easel in front of the child. Have them grasp a crayon, and try to draw a line UP the left side, across the top, and down the right side - one handed (no switching hands in the middle. Both up/down strokes are FINE, it's the "line across the top" that a LOT of ADHD kids fail, right where the line crosses the centerline of the body. There is a dificulty in the left and right hemisperes of the brain communicating. There is a structure in the brain (can't remeber the name right now) which connects the 2 hemispheres, and allows them to communicate. It doesn't WORK (in fact, they sent my son for a brain scan to make sure it's even THERE)

Now, generally, as a person with ADHD gets older, they learn to deal with it/learn coping mechanisms/partly to fully train themselves (as you said).

BTW It is thought (at least by some) that ADHD was a survival skill back in the hunter/gatherer day. As my son's pshycologist says "I have ADH...Hey, look, there goes a rabbit"