Willing suspension of disbelief
That seems to be the common factor in all of these tales: the intense desire of the teller to believe it, and to have us believe it in turn. They also can tell us a lot about our culture and society and that's why they are interesting to study. Often, if you question one, the relater will show a spark of anger and then will come out with the ultimate weapon-- "Well, my cousin's friend was THERE when it happened!" These myths evidently feed some need in us.