Hi again,
2nd question: the authors can add an explicit permission to link the GPL'ed program they wrote against some proprietary library or program.
2nd question explored further: if said library or program is something that is part of the proprietary system in question, then there's no need to add an explicit permission. This is _not_ the case of MatLab.
But how can a piece of software that does not even grant the first of the four freedoms ("The freedom to run the program, for any purpose") can be made Free? Really, I don't get it. If someone sends me a piece of Matlab code I cannot run it! What am I supposed to do? Convert it to C? Try to load it from Octave and see if I am lucky enough so the developer did not use any of the Matlab toolboxes?