The more authoritative, popular and related the site that links to you, the more valuable the inbound link becomes.
Because .edu and .gov sites are usually seen as more authoritative and reliable sources for information, IBL's become highly prized, especially if the link is from a TLD.
Get a link from the home page on a well respected, authoritative and highly popular blog site and you'll have one foot in heaven.
Look at it this way, if the link is buried deep within the content on some obscure page, several levels into a site, should it carry as much weight as a link from the home page?
A link to an old news item might look like this:
Code:
www.fancyimportantsite.edu/news/archives/date/section/subsection/newsitem.htm
A link to current news might look like this:
Code:
www.fancyimportantsite.edu/news/newsitem.htm
Obviously, old news (old content) won't get as much traffic as fresh news (new content) that's posted right off the home page (or one level down, as in the example), so you can see where the search engines are going to focus their attention.
Realistically, whether it's a link from a TLD or not, any link from a respected site is helpful whether the domain ends in ".com", ".gov", ".edu" or ".org".