You're saying the derivative work issue is specific to GPL because without GPL the application author couldn't distribute his application without the permission of the library author anyway, because the application is no good without the library and he would need the permission of the library author to distribute the library.
No, I don't. I said that according to copyright law only the copyright holder gets to distribute their code, and that vendors of proprietary libraries may charge run-time fees in order to allow others to do it too. Application authors tend to take advantage of that sort of arrangement for the convenience of the users of their code. Whether that makes the application a "derived work" of the library is a non-issue in this case; the library is presumably sold in order to be incorporated in applications, and end users typically don't get to redistribute the code in question to yet other people.
With a GPLed library, permission to distribute is already part of the library's license, and the authors of the GPL are jumping through hoops to try to enforce specific licensing conditions on the distribution of code that uses that library, which is an entirely different ball-game from the proprietary case.
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