Duel points are set up so that if a weaker player defeats a stronger player, then will get >1 duel point. If a stronger character defeats a weaker one, they will get <1 duel point. In my dueling experience, I've gained as many as 4 duel points by killing a far stronger opponent, and gained as little as .1 duel points for killing a far weaker player after I became strong. One time I lost 16 duel points at once, when a noobie challenged me without a word, then ran away. I accepted and went to find him, but ended up hitting Unstick, which of course also yields, losing me 16 dp (and gaining him 16, I'm sure).
I've seen some inconsistencies, though. One time I started a brand new character, and a friend did the same. Neither character had trained anything, but for some reason, I only earned about .5 dp for a win, and lost 2 dp for a loss. I suspect that dp value is based on relative training, not stats. My character must have started the game with higher skills, and his character with higher stats.
On the one hand, I think duel points are an interesting and somewhat effective measure of dueling success. However, it can easily be abused. I earned all my dp fairly, mostly by dueling hundreds of times in the DR with friends, and with all the battling in the Dwarvesbane/Dwarven Star war. However, someone could create a new, weak character, and have it kill their strong character over and over, and they'd rack up lots of DP quickly. Of course their strong character would lose DP just as fast as their weak one gained them, but my point is that they can be abuse dishonorably (just like many other aspects to PS).
-Drahlian