Which is cheaper to license on average? I'm inclined to think that Denon and Onkyo would go with the more cost-effective option. I'd be surprised if Audyssey costs more.
This is a guess, but I don't think they will necessarily go with the cheaper alternative. They can afford to put MultiEQ, or even the much powerful XT version, in very affordable mid-line receivers,
due to the economies of scale.
This is why I failed to find 2 ch pre/pros, integrateds, or stereo receivers with anything like it. Even if they cost thousands of dollars, the economies of scale do not work in their favor.
I guess what I am saying is that if you are Denon or Onkyo, you pretty much outsell most any other brand, and might as well offer the superior features that we all clamor over. A positive feedback scenario where they can remain up high in the food chain.