Here's the deal. It is possible to camp certain areas. In most cases, why would you want to? Most of the monsters you need to kill for quests don't drop very good loot, so a person camping there would be camping them only if he was doing the quest also.
In addition, camping isn't as important as getting the first hit on a monster. Whoever gets the first hit is the only person who can loot or get exp off the monster, so kill-stealing is not an issue.
The mobs that drop the best loot either:
a) spawn randomly in a given area and aren't quest requirements, or
b) are tucked away in the safety of an instance.
Instancing is the real answer to camping. The most powerful monsters, who drop the best loot of all, are inside instances. Whenever a player or group enters certain dungeons, they enter their own "instance" of that dungeon. Only they can fight the monsters in that copy of the dungeon, and only they can get the loot from the corpses. However, all of the bosses of an instance don't respawn when you kill them. You have to exit and re-enter the instance to bring them back. It's physically impossible to camp that type of monster.
I don't think "having issues with campers" is enough of a description for me to really know what he's complaining about. I've talked about how WoW works in my experience; if your friend is experiencing something that worries him, it would be nice to know what. Otherwise, relax; it's okay.