> Among these, that if we wish to produce any derivative works (under the GPL's definition of "derivative"), we must also release these under the GPL.

This is not quite correct, in my opinion.

Copyright only applies to your work, and works which are derivative works according to copyright.

You can't write a license that requires someone to release 'all' his work under the GPL, for example. (It may be different if it's a contract.)

That's just what the FSF wants you to think. Of course, it usually doesn't pay to go through the legal hassel to defend yourself from unjustified claims by the FSF -- thus it's an effective chilling strategy.

For more information, see http://www.law.washington.edu/lta/swp/Law/derivative.html