I've seen many webmasters that are paying higher amount of money for .edu and .gov ( at least trying to get from blogs ). As for me I really think that there is no difference if it .edu or .gov or anything else I want you know if there any certain proof that these link are stronger then .com and any other ext. links
I don't think that they are stronger because of the .edu or .gov in their name, but there are some pluses to getting links from those domains.. One is that they've usually been around since the beginning of the internet, so they probably have more strength on the search engines. Also most .edu and .gov are registered for as long as possible and will probably be around for decades to come.. Therefore if you buy a permanent link it could be there in 30 years