This is the essence of what Google implements. Links between sites are a form of user curation, user behavior (clicks, read throughs, bounce rate, etc.) are like inferred votes. The problem is, everything is gameable. Marketers abuse reddit as well, it just isn't quite as profitable as ranking #1 on Google. If a major search engine implemented a voting model, it too would spring an entire industry of "optimizing" for rankings via upvotes.