People who play D&D for the other two pillars get direct enjoyment from discovering new things, and solving problems through diplomacy. But does the game actively reward this? Especially in the most recent editions? The assumption that treasure and experience is earned through combat is almost hard-wired into 3rd edition, quest experience or no. (Not to mention that "congratulations, you get a 1000 xp story award" isn't much of an exciting reward, especially if your campaign levels up whenever the DM wants.)