If this were true, then student web pages would be a gold mine for SEO spammers. If it were true then I would have sold my web page for thousands, as would any student.
Anyway, the reason why some people think this is because these domains often hold popular web sites. When you think about it, a lot of people are going to link to a university site, or to a government website by nature. Some of the best links I've built have come from university and government websites, because some of the pages I've had links from have been very popular. It's absolutely nothing to do with their domain.