Couple historical misconceptions to clear up:
I've read a lot of history books that claim that the story about the Aztecs believing Cortes was a god was actually invented after the fact. The prophecies, the return of Quetzalcoatl, and all that were likely added after to make the Spanish victory seem more inevitable than it really was, and to make other tribes believe that their gods had forsaken them. If nothing else, the bad behavior of the Spanish would have tipped the natives off very quickly.
Secondly, most people think that Cortes and his small army defeated the Aztecs without assistance. I know that's how we learned it in my elementary school. We learned that just a few Spanish with guns--less than 1,000--defeated the entire Aztec Empire, with its hundreds of thousands of troops. However, doing some research later in my life, I discovered that while there were indeed few Spanish soldiers, they were accompanied by upwards of 200,000 native allies during the Siege of Tenochtitlan--other cities who were enemies with the Aztecs and agreed to fight alongside the Spanish. Basically, the Spanish just set off a rebellion. I would say that the 200,000 native soldiers were more of a factor than the Spanish in the actual battle.