Sun’s Open DRM

Sun has launched an effort to create an open DRM standard and open sourced one of it's DRM projects. I must be missing something but I don't understand how an open source DRM system would protect content. If it's open source, I can just modify the decoder to write out the unencrypted version of the file. If that's the case, I'm all for open source DRM since it would functionally mean no DRM at all.

**Update:** Cory Doctorow has the same question as me about open source DRM and he's read all the Sun docs and talked to the project leaders.