I believe if you had more demos of functioning network code (like, for example, the whole setup of joining, chat, kicking, disconnecting, rejoining, and, more importantly, movement interpolation and prediction) that would raise the number of sells dramatically. Examples that you could 1) learn from and 2) copy and paste, in part, into your project. The examples you mentioned sound good, but they're too basic. Everyone can setup a server and join it, after playing around for a few days. But when it gets to more advanced stuff, like smooth movement and shooting, people fail.
If I were you I'd make a basic, fully working, example game that is built up during the process of reading the book, including entity creation, deleting, moving, controling, but also level loading, chat and the like.
Also I'm missing serverlists. No gamer nowadays would want to connect via command line or IP address...

With all of that said, I like the idea of boosting the number of people who know about 3dgs multiplayer... and thus maybe the number of multiplayer projects.