This is a pretty common confusion. Here's clarification based on the rulebook:
I believe this commonly comes from having read this section and forgetting the parts in parentheses:
p. 20. "The Campaign Phase" ... 3. Receive Rewards: The overlord player and hero players each receive one experience point, regardless of who won the quest (as listed in the Quest Guide). Record this on the Campaign sheet. The winner of the quest receives additional rewards as noted in the Quest Guide.
So, what's happening is they read "Each player gets 1 XP + Whatever the quest guide says" which can be confusing. But the important part is that the "1 XP per player" is specifically mentioned as ALSO being listed in the quest guide. This is to give you a heads up that everyone will be progressing in the game, win or lose. Note that when using the side-quests, they DO NOT list 1 XP per player, and that is intended. Those quests are only for treasure / relics.
Edited by griton, 23 August 2013 - 10:57 AM.