It seems that Google's Web spam team is sick and tired of "Googlebombs," the practice of linking an unflattering phrase to a person's name to make a (usually political) statement. The classic example, where the term "miserable failure" was linked to George Bush's page on whitehouse.gov (and secondarily, to Jimmy Carter's page).
Google's Matt Cutts, in posts on the Google Webmaster Central blog and Cutts' own blog, the change was made by improving the way Google analyzes the link structure of the Web. Because the effect was small, Google has pretty much ignored them until now, but some people were under the impression that these Googlebombs reflected Google's own opinions, so they felt it was time to remove them, Cutts said.
The new algorithm doesn't erase all memory of the events, since articles like one this Search Engine Watch article from 2004 discussing the miserable failure" episode.