Well, we still haven't really tapped video, which is arguably a much higher source of data on lots of things (especially on how things act in the physical world

Well, we still haven't really tapped video, which is arguably a much higher source of data on lots of things (especially on how things act in the physical world). And curation will likely help a lot. And it's not like you can assume an indiscriminate crawl of the net is all human generated currently, anyway, let alone accurate. There's always cleaning involved.