That's disingenuous. All the emails I get from LinkedIn are unsolicited and I take my normal approach to spam of not responding, because responding only makes the spam more likely. A better example would be someone putting their resume up on a job board (not a professional social network) and ignoring all the responses, which I have trouble believing anyone does.

Don't you think that some people use LinkedIn as a way to be contacted for new jobs? I think based on the way profiles are written and optimized, at least a fair number of people use it as an ongoing passive job search.