it would make sense that the status of software A didn't change, but people are claiming that software A must be a derivitive of library B due to the fact that there is no other library that it works with, if there was another library then it may not be a derivitive of software B.
this is what isn't logical, and as others point out, is a very dangerous precedence to set.
it would make all free software that was written for windows derived from windows (because that's the only OS it was written for), it would make linux derived from Intel's 386 chip (because that's what it was designed to run on), it would give apple exactly the control that they want over all software written for the iphone, etc
such results would be nonsense, but the same logic that you are claiming for the situation where there is no code copied from a library into an applications source code would lead to these conclusions as well.
I may have missed something, but I haven't seen any court cases that implied or stated that this is valid logic to follow, and there are court cases (like the recent 'jailbreaking a phone is ok' case) that point the other way.
as i said before, besides being a dangerous precedence to set, I don't think it's needed, in part because I haven't see anyone try to use it (in anything other than public threats)