I doubt it would affect DVDs, since there's nothing in the DVD standard to mandate it, and I don't think that's up for renegotiation with the movie studios.
According to
Ars Technica, only some iTunes Store downloads fail. It's not clear why. I wonder if those movies would fail to play on any other Mac, since AFAIK no other Mac supports HDCP. Although HDCP over DVI is possible, I don't think it's supported by many computer displays. It would be a little odd if only the newer machines were restricted.