Instead of trying to protect data on the media, MediaDefender has completly new tactics. It wants to attack the peer-2-peer network where the copyrighted material is spread freely. It requires a lot of manpower and bandwidth, but it could be successful tactic.
The trick is in poisoning the shared data. As you may know, peer-2-peer system shares data in small chunks (it doesn't copy files like in windows), and after downloading all the pieces you can use the file(s). But what if one or more peers had a fake file that pretends to be the real one? This is one of the tactics MediaDefender is using that should result in a corrupt download. The company stated that they are going to trick the bittorrenting system.
The problem is that this requires a lot of man power. Everyone with a decent Internet connection can start seeding, so the guys at MD have to actively search for new torrents and try to poison them.
Because this is a really complicated process, the protection would last for the first two or three months after launch. This is the period when the revenues are the highest (new product) and when the level of pirating is the highest.
If you are interested about the topic, you can read more at ArsTechnica.