dunno, but it's pretty obvious that Google (and all search engines) are just trying to catalogue content in the most useful manner for the users that use it (that's you and me).
The SEO crowd have a different focus; they want Google to place their content at the top without any regard to it's usefulness to the user who is trying to search for a specific term.
In the past we used to find pages at the top of our search list with no possible relation to our search terms.
If you typed something like 'Travel' in the search box, the chances are the top 20 returned pages were all seeking to sell you cheap Canadian Pharmaceutical goods, for God's sake!
Where's the use in that?