DVDs are currently limited in their storage capacity. If the program could be off loaded to a harddrive in the DVD player, multi-level and multi-disc recordings could play through seemlessly. Won't ever be permitted though as the industry is too fearful of home piracy. Alternate branching in playback could be faster too (give the viewer the option to watch the movie's theatrical cut, director's cut, workprint cut, or extended cut).
Some planned DVD recorders don't even record to disc, just a temporary drive internal in the box.
I've heard that some digital video receivers put a block signal in the pay-per-view broadcasts that jam the video signal on recordings, even VCRs. The program looks fine when the original broadcast is watched but noticable every few minutes on playback.
Big Media does not like the concept of fair use/home taping (Hollywood didn't even like the Supreme Court decision in favor of Sony Betamax).