Wouldn't it, in fact, be easier to spot cheaters in a 1v1 setting. If someone is repeatedly running in and feeding 1 on 1 it's way easier for a GM in hiding to spot and screen shot. Also, any competitor could keep a feeder at bay. All he has to do is go into the room with an alt client or friend and sit there. If the 2 player room is full then no one can enter to feed, thus an easy way to counter feeders until a GM can be contacted.
I think a lot of you are missing something key. PvP stands for player verses player. Not player verses gang/ gang verses gang/player verses guild. An additional arena for 1v1 combat would be fantastic. Finally a chance to prove that you are truly great with just your class. No alt char buffing you or friends defending you. Additionally, people won't really be able to flee from a duel like in say for fild where they can just warp... Sure people could alt+f4 but there is a couple second delay before your character logs out in which you would die.
PvP ladder is to show that you are a great pvper. Not you and your friends, or you and your guild.
In addition: No one forces you to enter. You can still have your gang fests/wars in normal donation pvp.