Isn't exactly that the job of a search engine? I.e., that don't have to specify the exact site? Moreover, many searches are done be beginners who don't (yet) the best resource for what they search for.

But let's assume you use a search engine only for stuff you aren't intimately familar with - how could you trust the quality of the results? If they are so bad at the topics you know much about - why should they be better at the other topics?