Someone in another thread referenced a PubCon or other appearance by Matt Cutts where he pulled up an internal link checking tool and revealed that the effective links on the website he was 'reviewing' made up about 5% of its total linkage.
I regularly see the odd site on page one that has 10% or much less links by volume compared to the others. There's usually one in every niche I check. Those are the sites that interest me. Work hard, yes - but work SMART too. When you go through the links by hand you can see the quality.
It's not even a question of highly relevant from what I can see - just that the sites doing the linking are undoubtedly quality, busy, popular sites.