You guys are right, any type of media can be copied. We saw it with VHS, seeing it now with DVDs. The mobile device Apps may have a better run due to the hardware controls on the DRM (digital rights management). For instance, you can crack the DRM on an iPhone app, but then you have to "jailbreak" the iPhone OS to be able to use it. WAY too much trouble for most people, so it becomes more hassle than it's worth to copy.
DRM-enabled Apps on the iPhone/iPad and books on platforms like Kindle and Nook are getting more and more attention from publishers for this exact reason.
Another strategy is to find a way to create value even when media is "shared." One option is to use a blend of affiliate incentives, preview packages and value-add. For instance, say you're selling video coursework on a DOWNLOAD site. Everyone who buys the course gets instantly enrolled in an automatic affiliate program.
Although it does happen, most people don't try to profit by selling illegal copies, they simply share it for prestige, etc. So offer the ability to "be cool" by sharing the latest discovery, but offer a tangible incentive. Rather than share the actual media, have a "preview package" that can be shared along with the unique affiliate links. Then when someone shares the media they can earn cash or credits for the referral with zero effort on their part.
The trick is to make sure that there's additional value to actually purchasing the course. For instance, in addition to the video download file, paid customers also get access to a password-protected website where they can access additional, non-video course materials and perhaps even interact with other students and instructors. The last part makes sense if part of an online school or university model.
RE: App Content:
Apps that try to cover lots of ground are little more than a novelty. For instance, someone spent a ton of cash to produce an app called "Wing Chun Master," which was really pretty and touched on a lot of topics, but had no depth. Novelty.
The apps that are truly useful are very specific. To use the BJJ apps as an example, the good ones are designed to go right out on the mats with you as a practical reference while you're training. They're very specific. One app for sweeps, another for escapes, one just for leg-locks.
A JKD app wouldn't be one app, it'd be a suite of apps covering a range of different topics at different skill levels (theory and principles, foundation footwork, basic strikes, basic kicks, and so on.).