Where the GPL is concerned the distinction between linking when code has been compiled and the API itself is very clear. Code is copyrightable, but headers and interfaces do not make something else a derivative work. Stallman agrees on this one:

http://lkml.iu.edu/hypermail/linux/kernel/0301.1/0362.html

The code depends on copyrighted libraries, but, this has nothing to do with whether the method of calling a GPLed code library is itself copyrighted.