Google explains how crawl rate can be used as confirmation that a page is OK to remove from your website, and thus their index.

Please visit Search Engine Land for the full article.

Original source: http://feeds.searchengineland.com/~r/searchengineland/~3/NbJ77KwQ3Qw/old-content-still-showing-up-in-google-search-results-google-might-not-find-that-content-important-304052