In reply to alex.

creators of commercial plug ins could find themselves with no recourse against people who take their code and redistribute it for free, as the plugin should, to meet wordpress standards, be licensed under GPL

I heard of enough people having to pay damages for redistributing things they thought they are allowed to.

If you can not afford a lawyer on your pay roll it is better that you do not distribute anything you have not created or have explicit license for distribution. "but Matt said so...." type of defense will at most serve as a mitigation factor, but really just the cost of going into court is so high, that unless you are 100% sure in what you do, you should not take any risk that might lead you there. If a plugin is not explicitly GPL then just don't redistribute it or any part of its code.