This is what I received back from RR.
" We do make some new titles as compact disc only, but they are projects that we don't feel are appropriate for surround-sound which we include on the SACD releases. I do hope we don't lose you as a customer.
The CD layer on a hybrid SACD "should" not sound any different than a stand-alone CD release, we use the exact same DDP that we would send to a CD plant to make a compact disc. But I understand there may be something in your playback system that does not work well with the hybrid discs."
They do sound different as I have done the comparison, maybe it jitter count or something I'm not sure.
And there was a Hybrid disc that wouldn't even play the cd layer of the disc on my Esoteric Transport yet it would play a burnt copy of the disc when the cd layer was copied to a blank on my computer which played it.
Cheers George