That being said, I'd like to see if HN could provide some kind of fraud protection for upvotes/downvotes. I know that, for example, ad providers have some kind of algorithm detecting if the click is valid. Does anyone know of something like that in use in some of the community recommendation sites like HN?

As it is now, it would be fairly easy to game HN for karma or marketing reasons. All it takes for an article to take off is less than 10 votes at the right moment.