If the density is different, the material is different. Not sure why Cherry would deny it, unless they consider something in the same family of plastics to be the "same material".
Those pics are really awesome, thank you phoenix1234!
Anyhow, I don't think Blacks are the only ones with this "modern" vs "vintage" problem, although the material change would make it more obvious. All the newer Cherry switches are not smooth and need a considerable amount of use to wear in. On the tactile switches at least, heavy keycaps seem to help to mask the scratchiness, although it's still noticable.
Unless the material is very different, there's no reason I can see that really well worn in MX switches can't be as smooth as "proper" vintage Blacks. And I mean ALL the MX types.
I believe most of them show marked improvement after 50-100,000 presses, although I can't recall where I read it / heard it. I've been considering making a machine to "wear in" my Clears for me.