Actually, since the advent of the English language, Aboriginals do share the term Rainbow Serpent, but it seldom means the same thing region to region or tribe to tribe. In my area for instance, the Angel of Creation is often depicted as a multi-colored snake, being the most beautiful of all the angels. So, using the term Rainbow Serpent to describe the Angel of Creation is common here, but travel a few kilometers north and Rainbow Serpent is used to describe the creator God, (not the same as the Angel of Creation). Head northeast from there and you'll often hear it used to describe a rain yielding prosperity. Then go west and it's a fertility symbol. That's a fair point and one I've pondered myself from time to time, but here's the thing. The Aboriginal story of creation is primarily based on ancient paintings and artwork that predate the OT and the arrival of the white man. Now, the interpretations of those paintings may well be much more recent than the paintings themselves, but I honestly doubt the OT had much influence. For one thing, aside from cultural variation in the way the stories are told, they're otherwise very consistent among all the different tribes, yet they're not consistent with traditional Biblical teachings. I should think if the OT was the influence behind Aboriginal interpretations, it would be otherwise.