Haha. Technically that's 100% correct. The GPL is precisely what makes that possible. But can you imagine the amount of grief they'd have gotten for doing that? (Edit: and I mean grief from the general public, not the developers who actually(*) know what they're doing when they license their software.)
That is, more or less, what I meant by the above statement. You know this crowd, I know this crowd - if you were Valve, would you *really* want to step in the midst of the community engine people? Anywho, you definitely have spent more time reading the GPL than I have, so I have to agree when you say that it was all by the book. Overall, however, I still stand that the whole thing reeks a bit.