brinked - 5:11 am on Dec 8, 2011 (gmt 0)
I think a big part of it goes into sites being repetitive in their pages. For example if your sites main focus is widgets, you are going to intentionally (or in a lot of cases unintentionally) try to make sure the word widgets is mentioned anywhere possible. So then you have all your pages describing a different kind of widget. Well ok...now google may see this as redundant content. If your site is about widgets, It automatically assumes your article talking about blue widgets, is about a type of widget. The word widget does not need to be mentioned as it just starts to become assumed that it is talking about widgets because everyone including G knows this site only talks about widgets.
I do notice in several industries, the sites that received a major boost had sections on their site completely different than that mentioned on the home page. Google can see your homepage and right away see what your main focus is. If your home page title is labeled "Widgets" then G can then see if you are trying a bit too hard to rank every which way for widgets. But now if you also have an entire section devoted to tidbits and then an entire section devoted to ridgets you now have a diverse website filled with content that is not only related to widgets. G may see you did not place the words ridgets and tidbits in your homepage title so you created those sections for the sole purpose of it being useful to your visitors and not G.
Tidbits and Ridgets may not be widgets, but they may compliment widgets and users who are into widgets are probably into ridgets and tidbits. A lot of websites who try to game the algo usually have only one focus. There is a lot of money in widgets, so webmaster has motive to want to rank high for widgets. There is no money in ridgets and tidbits so webmasters motive is to provide useful content to its visitors, not profit off high paying industries such as widgets.