Search engine optimization isn't based on keywords alone. Importance is also a factor. "Important, high-quality sites receive a higher PageRank," according to Google, which uses its PageRank system to determine the best sites to display in natural search engine results.
"Google goes far beyond the number of times a term appears on a page and examines all aspects of the page's content (and the content of the pages linking to it) to determine if it's a good match for your query." An easy way to measure a site's PageRank is to visit a site like checkpagerank.net.