The major tube sites from the looks of things are primarily dominated by other sites trying to fight for traffic via branded videos, or by cutting a deal with the owner to have branded pages that not only showcase their uploaded content, but a few banners here and there to try and push half satisfied viewers to the core content hub.

I'd guess that the tube site is getting some sort of service fee for allowing the sites to have a "premium" service, as well as some sort of kick back depending on the conversion rate from leads generated by the content (why the premium videos are generally listed higher).

If you think that 1) the videos are legit and that guy just happened to stumble across those two girls in the woods, then you're also going to also believe that 2) most of the content is amateur. - It's a sad truth that the industry preys on the weak minded.

I'd say that a fair amount is self-uploaded (via content bought from providers, or produced specifically for the site), but a majority is uploaded from other content houses to try to promote themselves. Think Free to air TV... average crap shows, filled with 80% advertising.