From what I tested, it seems that XP modifier in DB applies to quest as well.
Anything can be coded in, if you know some C
A little off topic, but, in order to achieve the questing level of wow, you will have to put in HUNDREDS of new quests anyway, so modifying XP of existing quests is rather moot point.
Not to mention all EQ xp quests really sucked anyway - give npc 4 bat wings - what kind of quest is that?