The reason sites like Google and YouTube are good is not because you can search the larger sites well, but because they can search the long tail of the web well. Any search engine can index the top 5-10k sites and build something workable for that. The money maker is returning lesser known sites because, despite not being popular, they contain the best answer for the search query. YouTube got popular not because it has the most popular videos on the web (all video sharing websites have the popular videos) but because it contained and stored an insane amount of videos with like 100 views and would return them if you searched for something oddly specific.
I don't think search has much to do with YouTube's success. Just having all those long-tail videos is the main thing, and it has those videos because it's popular.
I've heard that a key early advantage of YouTube was that uploaded videos appeared immediately, not after a long processing delay. That helped it become popular, and once it was popular, it stayed popular and crushed the competition due to the network effect.
