Some askers may get lost just because the thread dropped off the bottom.

I expect some small fraction of the GUESTs who don't reply, did actually read your response, and neglected to answer either from thoughtlessness or due to technical difficulty. ("Hey, Joe, remember that question you wrote on the internet Thursday on Susan's new computer? She sent you this printout of the answers that came back. Isn't this great?")

Often, a later visitor expresses gratitude for the discoveries made at another's behest. For each of these serendipitous thanks there must be many visitors who read, smile, and go away humming, but don't speak up. I agree with Joe on the asker being only part of the audience, but we are all free to leave requests unanswered for any reason. Thanks for the research you do!