As you know there are still people who sell edu links. SEOmoz has a page strength tool which was free for some time. I dont know now but page strength included two strength factors; links from .edu and .gov.

I think the idea of the value of .edu or .gov links is the other way round. It is not that those links are more valuable just because of the TLDs. I think they tend to be better backlinks because many of them are actually trusted sites, the effect of Trustrank.

It is the same idea that a link from Dmoz is powerful as well. I have a blog that has a backlink from Dmoz, and because of it, I never lose the ranking within the top 10 even though I do not update the blog at all.

Another similar idea is also applied. A higher PR backlink can also push your website up a lot. Of course, in this case, you may not see a good result if a PR is PR4 or PR5. PR 6+ can get you a visible result quickly.

In any case, those links are still considered as quality backlinks. Indeed, you want few of those instead of thousands of junk backlinks.

*** Reply from Suzuki Kenichi ***
Do you think if .ac.jp and go.jp have an advantage as well aas .edu and .gov? It would be almost impossible for Japanese webmasters to get links from edu/gov.