Earlier quoted context omitted.
> Stupid question: If someone fixes or adds something valuable to GPL source code and wants to charge for it, then why not just charge for the patch or the additional code? Nothing stops anyone from charging for the GPL code in the first place.
True. But the idea I had in mind with this question was that there is often an initial free source of high value code and then someone may add an addtional amount of their own code that is by comparison far less valuable. The end user of the commercial product if it is closed source may not be able to see the extent of the contribution of that free portion to the value of the product as a whole. For lack of a better…
This violates the GPL. The skinned program is a derivative of the original software and must also be licensed to users under the GPL.