That isn't quite correct. A copyright applies to "works" such as writings, recording (sound and video), dramatic performances and software. It does not apply to ideas or, in magic, methods. It just means that someone cannot produce an exact copy of what you did. While someone cannot copy and sell or otherwise "publish"(e.g. on YouTube) a video, someone can legally (not ethically) teach a trick that is in a DVD by filming their own video.
You can still Claim ownership of it, and I think he was referring to copying a DVD, which is illegal under federal policy.
And you can actually claim a copyright on the pantomime around your trick. So the actual moves in an order, and the subtleties used with them can be copyrighted. This wont stop stealing and exposing it on YouTube, but it will limit it severely.
I think I have found a loophole that might be able to protect them! It's utilizes the trade secret law. Essentially, this is what I read about it (the exact example given, paraphrased a bit). "You Can't become Copperfield's Assistant and turn around and reveal all of his secrets to the public without getting massively sued.
Easiest thing to do is put a little box like this in the terms and uses, or just put it at the end of each purchase (or at the start of each DVD).
"By watching [and/or learning from] this product, you are considered an [assistant or whatever word fits here. Student, assistant... learner?] of this intellect under [Company or Teacher], created by [Creator]. By continuing to watch [and/or learn from] this product, you hereby agree to not reveal the intellectual [or entertainment, or whatever] secret taught through this product
to the public, without first having gained consent from [the company, or the creator or whatever]. Protected under the Trade Secrets Protection Act."
Now obviously that would have to be revised and find more things to put and stuff, but it's a start.
I'm going to make another thread for this just to get my point across!