Search for related content soon

Google has modified it's robots.txt file to include a line which may signal the beginning of a new search feature -- similar content search.  This innocent looking piece of text ("Disallow: /relcontent") appears related to "Disallow: /relpage/" which has existed in the file for a very long time.  Both URL's produce the same curious message when visiting -- "Nothing to see here!". 

Disallow: /relpage/
Disallow: /relcontent

Google already shows us a (less than stellar) list of related pages when passed a query like related:blogs.zdnet.com/Google.  In contrast to what it does return, I would expect it to show me other blogs with a similar subject matter -- like Google Blogoscoped, SEW or Inside Google.

It's unclear how this speculated feature could differ from the existing "similar pages" functionality --  I thought using "related:" was designed to find similar content already.

One possible implementation could benefit users researching fairly broad topics.  It may be easier to enter a paragraph or two of known information rather than picking and choosing keywords hoping to strike gold.  Does anybody remember Google Sets?