It's funny that you mention libreadline. CLISP was not originally going to be GPL'd and only optionally depended on readline, but Stallman himself declared that even that made CLISP a derivative work. I happen to agree with your interpretation, but the author of the GPL does not.
At the time, editline did not exist. Stallman's argument was that code which has functionality only when linked with GPL'd code is dependent upon that GPL'd code.
Indeed, this reminds me of all the OpenBSD discussions where Stallman tried to mark OpenBSD as a non-free operation system - fun fact: OpenBSD uses and suggests the ISC license, the most liberal of them all.
I would say that stallmans claims do matter, because failure to comply will get you labeled as an Internet villain. The impact that may have on your business will depend on the nature of your business.
Considering the vast array of bizarre and offensive views held by Richard Stallman, I do not think disagreeing with him over one more small matter will bring any great harm.
