I've never seen this said explicitly, but it's always been part of my thinking. A link that gets clicked is a link that is relevant within it's context on the web page it resides on. A link that gets clicked is also topically relevant to the site visitor, which makes it a kind of vote for the link. A click can be thought of as a positive signal of topical relevance. That is the kind of link search engines aspire to award 100% link pop in a citation based algorithm.