True, but if you also have many quality links pointing back to your site, its possible that a search engine can actually find your site by following them, without you having to submit your site at all. The amount of links your site has pointing to it is what makes it an authority site (besides domain age etc.), and also affects your ranking. If you used this on a lower level keyword that doesn't get many searches, you would rank your site well in little time, and virtually no on page optimization at all.