They changed this back in fathom days. I remember Loso had 40K+ kills (most kills) and he farmed kills in Forest Haven a lot. They later changed it so you can only get kills in zones at, or above your level range.

Quote Originally Posted by Royce View Post
This goes back to even before the swamps I believe, during the 30 cap or maybe early swamp days. Also I'm fairly certain you don't have to do any damage to get a kill. Just like XP, anyone in range when a mob dies gets a kill (I think, but maybe should double check...).
In PvE, I believe it is whoever throws the hit to kill the enemy. So no matter what everyone else does, if I get the killing strike, I get the kill, while no one else does.