I would imagine this is a cautionary tale for wikipedia. There is simply no good way to monitor the quality of a site that is voluntarily human edited. Wiki has some great content. But it also has a wide range of pure drivel.
I think Dmoz could have been successful and profitable. But they needed to pay the editors. They should have charged ten or twenty dollars to submit a listing, and then split that fee with the editors. To determine who gets to be an editor they could have continued to accept voluntary editors. When the volunteer hit a set number of listings published they would have had the money to evaluate the work, and consider promoting to a pay system.