This is an old topic from back last year, thanks to patch 1.12.1, but it seems that some players still manage to be surprised. A player posted the question to the Blues over at the World of Warcraft forums: "I don't understand the theory. twice upon abandoning a quest I lost the items I collected for the quest. Why? "

Answer, according to Nethaera: it (presumably) simplifies storage management for players and eliminates clutter by dropping all items from quests which are abandoned, on the presumption that players who've abandoned said quests are no longer interested in the loot that results from said quest.

(Another offered opinion, based on a Tseric post, was that this feature was added in response to players trying to stockpile XP prior to The Burning Crusade release. The rest of the article proceeds from Nethaera's answer, and not this presumption, but we felt it had to be added as a nota bene, just in case. A few posters in the thread are crying over Nethaera neglecting to mention this.)

Ah, but that logic Nethaera offers runs counter to one of the most iconic concepts of the gaming universe: the RESET button. Some - well, MOST players actually do the erase-rewind because they botched and would like a second crack at the challenge. In the case of our hapless player who found his pockets empty after abandoning a quest, he did so because he wanted to regain a ray gun whose timer had run out.

These kinds of players kind of resent, or at least deplore, that they can't keep the items they want to keep after abandoning a quest - again, on the basis of erase-rewind. Others find the "abandon = clear inventory" feature useful because, well, they don't like to be bothered by the details of going through the backpack for litter.