Hi there Alan (et al),
Thank you for the little blog post on me. I hope I can respond with some good, insightful (incite-ful?) posts to keep you interested.
Congrats firstly on your anniversary.
I consider myself a lay-expert (in other words I spent way too much time on slashdot for my career's good) on GPL so I'll add in my 2c.
The GPL severly restricts what you can do with the source in order to try keep the source available. It is known as "viral" in that if you want to use the source in a project - all the source of that project must also be GPL or compatible.
The big news of a project being GPL compatible is that once the source is GPL compatible it can be added to other GPL projects and in turn other GPL code can be pulled into this project.
Being GPL compatible is also a nice buzzword to use. And it would make coding easier - "Oh, its GPL. I know that". (No need to read the license and compare it to GPL to understand how compatible it is.)
I'm not sure exactly in this case how it benefits everyone but the above may give a good idea of why GPL is better to have than just "open source".