They own the treatment, yes, but they also came up with the original idea and they paid very handsomely for my take on it (do kids still say "very handsomely"...?).
This definitely is not some case of "oh, poor me, they conned me out of my ideas and I got nothing." They were great, I'm better off, we're all happy. Really, if I broke it down to an hourly rate, there's a strong argument to be made that I took advantage of Amazon.
And I'm okay with that.