Right. Because humans, turians, and krogans don't have any element zero on their world, they didn't develop the ability naturally, and have to be exposed in-utero to gain it. Since there isn't any other known way of gaining biotics (yet), we have to assume the asari's homeworld has element zero in it, probably its core, to explain how they developed it naturally. There might be a different explanation in ME3, but until then, that's the best guess any of us can make.
Then again, we won't really know just how inconsistent the story of the Reapers may or may not be until ME3, either, so arguing about either case is kind of pointless at this stage.