I've been meaning to mention that I looked up some of the lore online, and it turns out there is a reconciliation, sort of, between those stupid turtles giving people their bending and learning it from the moon/moles/air bisons/dragons. It turns out that the magic turtles thing was meant to predate learning from the animals. They stopped giving people bending at some point after the flashback we saw, and only then did people turn to nature to learn bending. I guess that works out, but it still feels very lazy to me. Deus ex machina, like I said earlier.
Speaking of lame explanations, the accepted reason for Zaheer being such an awesome airbender seems to be that he was just such a huge fanboy of airbending lore and culture that he already had a great "theoretical" understanding of how to do it, and he taught himself the rest. How disappointing.