I think the Compendium said a little something about it being on by default for PC and off by default for 360 and PS3. Or vice-versa, I only read it once.
My answer remains valid, regardless.
BLASPHEMY!
And I see it too, looks like -16 xp, -16 xp, -11 xp. I'd very much like this, because there are people who honestly do not care if they kill teammates. If they get kicked, they'll just find a new server. Losing hard-earned xp, however, is a major deterrant.