This doesn't directly answer the question at hand, but is somewhat related, take it for what it is....
The following is a quote from "The Story of Philosphy" by Will Durant.
It is part of the chapter on Plato. Plato is describing is vision of a utopia and one of the aspects of this utopia is for the leaders to create a religion. Plato wrote about the utopia around 387 BC.
Now since men are by nature aquisitive, jealous, combative, and erotic, how shall we persuade them to behave themselves? By the policeman's omnipresent club? It is a brutal method, costly and irritating. There is a better way, and that is by lending to the moreal requirments of the community the sanction of supernatural authority. We must have a religion.
Plato believes that a nation cannot be strong unless it believes in God. A mere cosmic force, or first cause, or elan vital, that was not a person, could hardly inspire hope, or devotion, or sacrifice; it could not offer comfort to the hearts of the distressed, no courage to embattled souls. But a living God can do all this, and can stir or frighten the self-seeking individualist into some moderation of his greed, some control of his passion. All the more so if to belief in God is added belief in personal immortality: the hope of another life gives us courage to meet our own death, and to bear with the death of our loved ones; we are twice armed if we fight with faith. Granted that none of the beliefs can be demonstrated; that God may be after all only the personified ideal of our love and our hope, and that the soul is like the music of the lyre, and dies with the instrument that gave it form: yet surely (so runs the argument, Pascal-like, of the Phaedo) it will do us no harm to believe, and it may do us and our children immeasurable good.
The similarities between Plato's concept of a utopia and modern day life are all over the place, its amazing to read Plato's work while keeping in mind how long ago it was written. He came up with things like education for all children until the age of 20, teaching art, music, and physical education along with more standard knowledge - he also described different stages of weeding out students. The first one being at the age of 20, were everyone would take a test and the majority would fail and those who failed would then be sent off to work as physical labor type workers, while the smaller percentage who passed would go on to higher schooling - then take another test at 25 - the majority would again fail this test and go on to work as higher professions, and the ones who passed would attend even more schooling and eventually become the government, or the leaders of the land. Of course the government hardly consists of the brightest people now days, but the idea of going to school till around 20, then some going on to college, and others going to graduate school seems to be bassed on his model. I believe that most western religions were put into place by past government or republic leader orginizations bassed on Plato's utopia vision. I believe that one man has changed the world more then anyone else by simply writing down his thoughts.
Perhaps religion was created by the want of people to create a utopia to live in. They wanted to create paradise. Religion as described, lying to people in order to get them to behave may seem like a negative and harsh thing to do, but then again the alternatives back then were either living in a chaos with no order and no production - or living in an orderly and productive society but having the draw back of the population always being in fear of and hating its leaders, because they would have to use physical force and punishment in order to get them to behave. So Plato's concept of controling the public with religion seemed to be a much better route. However I don't think it was ever as successfull as Plato thought it would be, because there were always those who would reject it and would still need physical force and punishment in order to behave. But then again it was successfull in controling a large part of society. So it did result in more imediate freedom then not having any religion at all. But not total freedom of course, because any way you go about it, these people were being controled by fear, whether it be fear of the club and physical punishment or fear of the higher mystical power - fear is the main factor in how populations through out history have been controled. Then again religion works on different levels for different people, it may have controled some by fear, but others may have followed suite bassed on the want to go to heaven, or the want to please their creator. As now days it seems the want aspect is the only power religion has, as people who would of in the past might of been controled by the fear of religion probobly now days don't believe in religion - so instead are controled only by the fear of punishment, or maybee not controled at all.
Regardless I think the answer to "why" religion exists, is as a method of controling the population. Free will has been the worst enemy of governments and kings through out all of history.