What I'm trying to point out is that you're talking about how important the XP is to people, that the reward is critical, that it's how human psychology works. And I agree. But if this thing is so important to people, do we think that it suddenly becomes unimportant to them when they're wondering whether they should go back and kill the guards after sneaking into a castle for the extra XP. If it's so important to players, if it's an inherent part of human psychology, then it's going to affect how people play.
Now I agree with you that if the game is about killing monsters, then it makes sense to get XP from killing. It makes sense in Diablo. It makes sense in ADOM. But the developers here have said they want to make a story focused RPG with strong noncombat abilities. That doesn't mean that combat isn't important - it's very important. But it's not a game where the player is encouraged to slaughter everything they see, like those games are. They can still do that - but it's not elevated above other options.