It's annoying, but they get no rewards, and they have to live with leaving in the middle of a fight, and proving that the person they are fighting is better.
:)
Then again, most campers and combat loggers do what they do because their is some kind of reward. Bragging rights. If you see somebody with an insane KDR (for example: 300 kill to 7 death = 42:1), it's probably because they combat log. Sure they might be decent at PvP, but there's somebody better than them out there. Or if they make a stupid mistake. You never know.
For example, my stats in duels is about 800+ wins, 600+ kills, 200+ deaths (although about 30 of the deaths belong to encounters with hackers and dying because I lag out). So basically my kdr is 3:1, I highly doubt someone with an insane KDR is legit or a person who goes through with the game even if it's clear they are out matched.