The girl was less of an angel and more of a example of the "vitality" of Mohammed. Then I guess in that sense, the "vitality" of Mohammed would have to be matched against the guaranteed purity of a very young girl.
If we look again at the history lesson in #16, it sounds much more like a classic "state marriage" arrangement, and that the subsequent spin was added on after Mohammed's death.
Let me be blunt as explained to me by a Muslim. The fact that Mohammed was an old man and could maintain an erection sufficient to deflower a 9 year-old is impressive to Muslim men. I'll be surprised if they didn't fly the sheets from the flagpole.