I've never managed to hear the artificially-created "cave" or "hall" effect that *some* report with either the CD3000 and occasionally the R10. I think sometimes people see a closed can and want to imagine there must be reflections or resonances or whatever. (Yes, I acknowledge that some people can hear this, until we can swap ears, we'll never know what anyone else is hearing.)
I call the R10 the "disappearing headphone" because when you close your eyes, they just evaporate from your head. I'm just not aware of the enclosures at all, nor am I aware of the drivers. I believe this is also in part due to the fact that the drivers are so far away from your ears in the large R10s, you aren't always reminded there's this little speakers milimeters from your ear pumping sound into your ear canal. Anyway, I've yet to hear any reflections or "wooden" sound of the enclosure or whatever.
I think the real question is not "why do these closed cans sound so much richer and lush", but "why are certain open cans so airy-fairy, insubstantial, light-weight and floaty?" Coming from an open can, the CD3000/R10 will trump them in terms of "presence" and body, but that's not a "fault" or a "flaw", IMO it's an advantage.
My over-used explanation for this effect of open cans is that listening to some open cans can be analogous listening to a pair of speakers suspended over a dry lake bed. I suspect this adds to the pastel "airyness" and overly dispersed and non-specific sound of a certain open can. Some people may prefer this presentation, others may not. A closed can creates a small pocket of dead air in which the sound can unfold, this lets you hear smaller more subtle cues in the recording that indicate the size, shape of the room in which the music was recorded.
Mark