Can't exactly do that in WoW except maybe in a party and even then, the person has to tag the body and leave the loot on it.
It doesn't bother me because I tend to know the value of the items in a MMO I play and know if it's worth going over my weight / another bag slot space. When you're farming a dungeon/place over&over again and it comes to having to leave early just to sell a little bit's worth or push forward for the EXP... well, EXP tends to be more value than money ^^