The idea may not be, but the moment it becomes a demo it can be worth quite a lot. The story, characters and gameplay can be very valuable, it is how the idea is sold to publishers. This is just like scripts in the movie industry. Most publishers have internal studios, that could possibly be sitting idle. While it is not often done, there is the opportunity for a publisher to move on a developer's idea much faster than the developer could.

The video game industry is brutal, especially with people doing copy cat projects. Look at the current farm games on facebook. The first one was FarmTown, made by a small group. Now some of the facebook powerhouses have released the exact same game with nearly identical gameplay and even similar art (FarmVille from Zynga and Country Story from Playfish).

Or just look at the rivalry between Rock Band and Guitar Hero.

The execution is still worth much more, but I think there is still a need to protect the idea.