.com .us .edu .ws they are all the same in a general manner. If you put the same .com against the same .edu with the same backlinks and content then there is no difference at all. The difference is a higher percentage of .edu sites are high pr because they are school sites most of the time. Don't go looking for .edu links, but instead links that relate to your topics.
In my opinion, edu's aren't so strong because of that they are 'edu's' but they have usually (in the majority) good and original content which can pass good energy for related sites. But that's just my theory