He left the code open and has allowed people to do what they want with it as long as they credit him as the original author. That's enough - if someone had the skills and motivation to actually work on it and not just version patch it, they could pick it up as long as his name was on the thread.
I've always had problems compiling java, but I can see how it would be simple. The problem is that as long as people make these outside of him, it's difficult to find ones you're sure work correctly. Different people make these versions, and they get buried in the "HOW TO INSTALL!" guides. It was a while before I found that 1.3.2 installer, for example. You just lose track of these versions. :(