It's a valid USP and people are happy to pay them for it, but I don't think they are relevant in a discussion about the difficulty of building a search product.

For example, if you are discussing manufacturing issues in China, talking about how good drop-shippers on Amazon are is irrelevant.

Tomorrow Bing could say "yeah no more index for you" and DDG shuts down. It doesn't feel like a very stable business model to depend entirely on someone else's business.