NOTE: Now that I have read the official BANG FAQ, I am not sure if this strategy is legal anymore. Read Question 23:
Q23. If an Outlaw plays a Duel and loses, does the player who won the Duel draw the 3 cards reward?
A. No. The reward goes to the player who played the card which was responsible of the elimination of the Outlaw. But since that card was played by the Outlaw himself, no one can gain the reward.
While this clears things up, it is still confusing. The card responsible for eliminating the Outlaw is not the duel, but the BANG! card that another player used to respond to the duel. After all, the other player did not have to play the BANG! If so, how was the Duel responsible for the death? It provided the opportunity, but that does not mean it was responsible for my death. I dispute this reading, and think it can be played either way (house rule at least). It does open up a new interesting strategy. You can duel anyone when you are at your last rope, not respond, and no one gets the card bonus. Thus, a duel suicide is still useful; you just can't help your buddy under the official rules. Though it may not be a rule, just a FAQ, as I think you can read it either way. Under their reading, Dynamite explosions should give you card bonuses too, as the player laid the card that was responsible for the elimination.