Here's a quote from the relevant part: "While a lot of what you see on our results page privately incorporates content from other sources, including our own indexes (e.g., Wikipedia, Local listings, Sports, etc.), we source most of our traditional links and images privately from Bing (though because of other search technology our link and image results still may look different). Really only two companies (Google and Microsoft) have a high-quality global web link index (because I believe it costs upwards of a billion dollars a year to do), and so literally every other global search engine needs to bootstrap with one or both of them to provide a mainstream search product. The same is true for maps btw -- only the biggest companies can similarly afford to put satellites up and send ground cars to take streetview pictures of every neighborhood."