Seems pretty clear that this falls squarely within it's right to regulate. Unless you can explain how the Internet isn't "communication by wire or radio".
But... everyone knows the internet is a series of tubes and therefore neither wire nor radio.
Estoppel comes into play. Check it. For one moment lets go all hypothetical and say that what you're suggesting is true, and that the MPAA and CCA broke the law horribly by denying people fair-use rights. Well, they can then claim that they've been telling people for years that the discs are encrypted (which they have) and that any challenge on this ground these years later should be effectively ignored on the grounds that "the public knew we've been doing this for so long and said nothing."
Could that point be argued in court? Probably. But a good lawyer would pad the estoppel claim with many others just in case someone did manage to shoot it down.
Disk crisis, please clean up!