Interesting story on how that happened. A class was touring Scaled Composites last summer, about a week before SS1's first X-prize flight. The students were talking with Burt Rutan and poking around the hanger. He said using NASA's B-52 to drop his ship was so expensive, that he decided to build his own plane for less money. One of the students, who worked with X-37 (which was having many funding problems at the time) asked how much cheaper. And, you see the results here.