*cough*
Deus Ex, Vampire: Bloodlines.
Dang, the best RPG's ever all have this mechanic too. Must be something there.
Also look at how everyone avoids combat in those games... wait; no, they don't.
But I've discussed all those fake strawmans too much on Obsidians boards to repeat it here.
Okay, humour me. Give a single instance where XP for peace is higher than for war. Not including cheatery double-dip "get charisma XP then kill them all anyway"...