Wow, I've never heard of someone betraying in WZ for a Nornfang or other mythic weapons. I definitely know there are some idiots out there who would do it... Just never heard of it being done until now.
BTB, Infection, Arena, you name it. All of those have multiple people who will team kill for power weapon, or maybe just kill you for the fun of it. I recently had a game in BTB where this guy would not stop following me and shooting me in the back.. He got me killed several times, none of which were actually credited to the guy. Needless to say he didn't get booted because he "never actually killed me".