Search engines ranking with nofollow
The nofollow attribute (rel="nofollow") is used by webmasters to control what search engines crawl, and can reach. The Google Blog explains that
It is quite interesting how the post mentions that it "isn't a negative vote for the site where the comment was posted" and uses the word site, not page. They don't say that the words surrounding the link or the page the link is on has no negative vote or a less of a positive vote.
From my point of view, any page on a site that uses the nofollow attribute says that it is ether less authoritarian or may not be approved by the search engine.
If the links on a page contain the nofollow attribute, it tells the search engines that the information is likely to be submitted by someone other than the webmaster. It could be anyone, and my be
spam. This means that the words surrounding a nofollow attribute like are more likely to be created by a spammer or someone who is less connected with the site and therefore can not be as much of a
trusted source. Why would search engines want to link to content that is not from authoritarian sources? (over trusted sources)
Not approved by the search engine
A page that contains the nofollow attribute could also be seen by search engines as possibly linking to pages that are not approved or liked by search engines. If most of the links off a website contain the nofollow attribute, the search engine could have the "if it is not good enough to crawl, then it is not good enough to rank" frame of thinking.
What search engines imply and do can be different. In 2001, Inktomi let it slip that pages rank lower if the url is manually added. They did not say anywhere that the pages found by the crawler had an advantage, but they did not deny it ether. A news release stated in 2001 that:
Inktomi is indeed penalizing pages submitted via the free Add URL system, the company says. "The free Add URL is very much a magnet for spam and low quality pages, so we do intentionally give those pages a lower ranking," said Michael Palmer, chief technical officer of Inktomi's search services division. The change was made in the middle of last year, Inktomi says