Tom BortelsI'm not sure "closed" is the right word. Clearly it's not closed if you are providing it - it's right there, I can read it and even redistribute it without burden.
It's "copyrighted", not closed. You can't modify closed source because you don't have the source. The assertion being made is you can't modify GPL'd open source without accepting the license. But copyright has its own carve-outs, and I am unconvinced that writing a spec or net-new code is a modification, as opposed to regular old copyright fair use.