My theory is this:
Women are created this way for a very good reason;
it's to ensure the survival of small children!
Anyone who's had experience with trying to instill good behavior habits in a child should understand. Do you know how exasperating it is to have to say the same exact words, perform the same exact actions, try to get the same point across over and over all day long?! Perhaps for days or even a week or two in a row? If a woman wasn't set up to "nag", she wouldn't mentally survive and would a child survive at all?
I've noticed that children get into "stages" of certain behaviors for a period of time. We obviously (to me) begin this way to make training more effective. Children, maybe adults as well, need practice to make behavior into a habit. When kids demonstrate the same type of misbehavior consistently and get the same response - not allowed to get away with it - they learn what the requirements are.
The problem is when we (anyone really, male or female) gets into the habit of responding to EVERYONE as if he or she is a child needing to be trained. As a person matures, he or she should be training themselves in right behavior. Teaching, guidance, reminders, consequences: these are what replace the early methods. Using these same early methods on an older child or an adult (a husband!) is now nagging.