... why are people want it so bad? I know this might sound stupid, but I really want to know : What are the benefits of having high PR (besides selling links)?
Well I think you gave the only reason people want a high PR. Is to sell links and nothing more, it gives them some number to say yeah I am linked by the search engines. Honestly though I have a PR0 site with 0 links to it and it gets search engine traffic through some of it's keywords although not super popular it still gets hit by search engines.
PR doesn't affect SERPS. I've got a PR0 website that is ranking on the 4th page of google for a popular keyword. Thats through good link building and unique content. Peopel want PR so they can sell links on their sites, like you stated
the PR reflect the general quality of the whole site , not a single page . so some pages will take better position in rank ,others will be in the last pages results
Both artificial PR and nature PR are more related to backlinks. SERP is one way to gain traffic; you also need to have the right keyword(s) for top SERP. To create backlinks is another way to reach more web traffic by being exposed at right places. Sure there are more other ways to achieve high traffic.
To be use in exchanging link. Some webmasters required to have a good PR if you want to exchange link with them. They require this in order that your site will also pass link juice same as what they've pass to you. It can hurt their site if they exchange link to a site that has a lower PR.
Are you sure? PR stands for PageRank, it ranks every single pages, not the whole site. yeah, I'm one of them The importance of PR is still remain unclear to me. So what will I get if I have a high PR site?
hi PR is definitely by 'page' and not for a site. The home page is not necesarily the page with the highest PR for instance ... but usually, the deeper you go inside the structure of a site, the lower the PR, since it gest 'diluted' each time. A site with a pr N and with a roughlty similar content as another website with a PR N-1 (N-2 ...), will be more likely to appear on top. For some very competitive keywords, you can't expect appearing in the search results if you don't have a significant PR (displayed or not!!) which means there are many other (quality) sites linking to you. So to me the PR which is displayed in the green bar is just a "potential", then, if you want to appear higher and/or with more different requests, there are other stuff to look at