Hii Guys, There are many topics which we can discuss in SEO. W3C standards are made for different type of tags like XML, XHTML, HTML. W3C standards are provided by World Wide Web Consortium to create a structure of websites. We can't say that W3C recommendation increase website PR but the chances of getting good PR can be increased. Because there are many other issues which are related to it like designing of website.
The information is really true. Also the visitors on the site will also get to know the authenticity of the site. As such sites with W3C validation would have good impression on Search Engines.
Yes I agree that W3C validation will helpful to some extent, to increase pr and traffic for a site but other factor like (link building, article posting, blog commenting) and many other factor can't be neglected..
I don't see any reason why the validity of a document would effect PR unless it's because people aren't linking to you because of it. On the same token, it's a good idea to try to adhere to web standards.