.edu sites can be considered highly authoritative for Google, that is because only universities can have a .edu domain.
The only thing that makes a .edu site special is that high authority sites tend to link to them. Think about it, what kind of content do .edu typically contain? Highly informative and educational content, and that is the kind of content that people like to link to.
IE if I wrote on a subject on SEO I may decide to link to a page that has been published on a trusted site such as seomoz, searchengineland and so on, these are authorities for a specific niche.
If I wrote about how Google?s Pagerank patent was approved, I may decide to link to a page from stanford.edu as that is where Larry Page first came up with Pagerank.
While anchor text is beneficial, the authority of that link could be even more beneficial.
If that comments page is linking out to low quality pages then a link from that page will become less valuable.
If we look at the correlation data from the seomoz search engine ranking factors you?ll see that authority of a domain outweighs anchor text links http://www.seomoz.org/article/search-ranking-factors
You should also note that anchor text links from external sources have had a massive decrease in effectiveness in the last year.