> "Oh, well, you always take care of it."
I've found that it's almost never the case that there is no division of duties. Sure, there may be no explicit division of duties, but there is almost always an implicit division of duties. If Person X is always the one that handles Task Y, then the team will come to view Task Y as a duty of Person X. Other team members may then just simply assume that Person X will take care of it, or they may even actively avoid it to avoid stepping on anyone's toes.