Firsty of all, after reading a bit more the 4C docs, I come to think that AV content tagged with CPRM is not necessarily encrypted - don't ask me why.
Then, I did a little experiment with the protected disk that's in my possession at the moment : I put in a DVD/HDD standalone recorder from Panasonic, a really new one (still on the store shelf . The recorder agreed without a problem to copy the protected movie to its hard drive and then to copy it back to a blank DVD-RW disk and also to another blank DVD-RAM disk. This is driving me crazy...