it seems that yahoo also now focusing on your main content, as you most of the sites have irrelevant or unimportant content compared to the main site content. If you want to check or experiment this, just use robots-nocontent tag on your pages
Maybe links to the sources for some explanations would be useful ? http://www.ysearchblog.com/archives/000444.html http://help.yahoo.com/help/us/ysearch/slurp/slurp-14.html http://searchengineland.com/070502-132315.php