I believe that PR doesn't give higher value in SERP, but why does other site buy links from other sites that has higher PR?
PR is one of the important factory in SERPS but not the only factor. Hope that answers your question automatically
There does seem to be some linkage between PR and SERPs. It is just one factor, but it is a factor, according to Google — "Pages that Google believes are important pages receive a higher PageRank and are more likely to appear at the top of the search results" (http://www.google.com/corporate/tech.html).
let say you site keyword is "web hosting" and you get pr7 link with anchor text web hosting and link to your hosting.. this keyword will get good ranking in search engines. cheers
PR indicates the quality of a certain site. The higher the PR, the good quality the site has. Having a backlink from a high PR site will surely help to build up your site.
I think people are puting too much emphasis on PR, yes people do think sites with high PR have higher authority but stats have already shown that having a higher PR doesnt unnecessarily mean you will get a higher search engine ranking.