Quote from athalnorUse of an API doesn't constitute creation of a derivative work (if it did, there'd be no way for anyone to create non-GPL software that ran on Linux, for example).
This whole policy seems massively overreaching, if you ask me. You could theoretically create an addon that doesn't even have a hard dependency on WoW (just use the base lua libs, etc). You couldn't do much of interest, but that's beside the point (well, not to end-users, anyway).
The main lua source file for such an addon would undoubtedly be your own copyright, and thus you have the right to do whatever you want with it, license it however you like, and charge whatever you care for it. Does adding a .toc file to the distribution now instantly hand your copyrights over to Blizzard, and give them the right to dictate your licensing terms?
IANAL but i found a PDF by one.
It's about the GPL and the "fear" of the GPL infecting derivative works.
Simply combining a copyrighted work with another work does not create a derivative work. The original copyrighted work must be modified in some way. The resulting derivative work must itself represent an original work of authorship. So if the licensee doesnt modify the original GPL-licensed program, but merely runs it, he is not creating a derivative work.
Consider the scenario where the Linux operating system, a GPL-licensed program, loads and executes a proprietary program. The Linux program is not modified; it is merely used for the purpose for which it was designed. The proprietary program does not contain nor is it derived from Linux. Linux does not infect the proprietary program, and the proprietary program does not become subject to the GPL.
An even more tenuous relationship is established between programs that interact through data using a published application program interface (API).
Simply passing data between two programs, even if that data influences the behavior of those programs, does not create a derivative work of either program.
While the document is about the GPL, the arguments are based on copyright law, which cannot be modified by -any- software license.
A derivative work is defined in the Copyright Act, 17 USC 101, as a:
work based upon one or more preexisting works, such as a translation, musical arrangement, dramatization, fictionalization, motion picture version, sound recording, art reproduction, abridgment, condensation, or any other form in which a work may be recast, transformed, or adapted. A work consisting of editorial revisions, annotations, elaborations, or other modifications which, as a whole, represent an original work of authorship, is a derivative work.