I think what happens is that eventually there aren't enough "good" links out there that haven't been submitted, but there's still a demand to be filled. Newspap

I think what happens is that eventually there aren't enough "good" links out there that haven't been submitted, but there's still a demand to be filled. Newspapers keep "filler" stories around for that eventuality ("slow news day"). I think the same thing happens on social news sites - especially ones that grow - because the demand (for new stuff) eventually outstrips the supply (of good new stuff).