Eine gute Erklärung gegen Opensource steht noch im FAQ:
Why don't you make your games open source?
Our source code is our livelihood and we have to protect it as our most precious possession. While we believe in the open source movement to an extent, if we made our games open source, we wouldn't make any money and wouldn't be able to do this full-time, so it would defeat our purpose. However, we may do some code discussion on the member page of the site for those who are interested and we're always willing to talk about game programming in general.
