Information can easily become extinct. I imagine what it would be like if someone asked this question in 75 years, and there was literally nobody alive who could help them identify the microphone's originality (regardless of the price offered for such a service).
(…) And the knowledge passed on does not cost you directly, apart from the time taken to impart it.
Maybe Klaus has suffered financially for the information he has given out for free, but I suspect the gain in new customers and reputation easily makes up for those losses.
How did you acquire your knowledge? Did you have to pay for it? Or did you follow the experts before you and try to expand and build on their most often freely shared input? Isn't the open exchange of unique knowledge and information one primary purpose for the establishment of any forum?