Some people like getting ribbons and medals and such attached to their record. Theres never been in-game rewards that I recall. Traditionally, everyone involved with the kill / group could get kill credit and while in say UO, this was probably a good thing UO pvp was relativly small-scale compared to a Siege-warfare type game. Giving individual kill credit for army size engagements would probably be alot of unnecesarry paperwork.

On the other hand, I think for smaller scale engagements officially recognizing good squads and groups that perform well, take out enemy raiding parties, raid enemies territory etc should definatly be recognized.

Personally, I've never really concerned myself with kill-pic medals even in UO. Crushing ppl in-game is its own reward.