I'll watch the video some time, can't right now.

But yeah, pretty sure a patent has to do with it. I mean World Of Goo is a pretty good game, and giving the source code away just like that would let someone make a clone without much effort, yet make money from it. For example, David or someone could make a World Of Goo version that allows extra chapters to be added, then sell it to people.
In any case I wasn't surprised that the source wasn't released. How many non-free games do you know that have released it?

Quite a whole lot, actually. In fact, that's the whole point of Ryan Gordon's talk in the video.
What I meant was that there was some kind of nonfree software that 2DBoy did not write that they could not release the source of, and therefore couldn't legally release the source of their game. Otherwise they would have.

Ah, OK.

By the way, would you mind mentioning some of those games that release the source? Maybe I know them but just don't know they've released it.

All the other HIB1 games: Penumbra, Aquaria, Gish, Lugaru, as well as a bunch of id software games: Doom series, Quake series, etc. Those are the main ones he mentions in the video.

Oh, cool. I'll have to watch the video sometime then.

You know, if 2DBoy realesed the source under GNU GPL license, no one could use that to make another game because if someone use the source, and modify it, he must publish under GNU GPL, and he can't sell it.

True. But anything made from GPL source has to be GPL-released itself, so the game would have to be free. Even if it weren't, anyone could compile the GNU source and release it under the GPL.

Personally, I don't really like the GPL. I don't like being told what I can do with my own source code. I prefer the MIT license, which can be summarized as this: "You have to give us credit, and you can't pretend that your modified version is the original."