This subject generate always controversy Bogart.
PR play very little perhaps nothing. I have seen many sites with PR0 ranking #1 for their keywords and the pages could be content or product with SEO link anchor texts properly made.
What difference does it make to have pages with PR or without PR if you rank for your keywords in position top #10? The goal is ranking high as much as you can to be visible. Now if you are selling links on PR pages that's unethical regarding Google guidelines. So what's the deal to try to manipulate the PR system beside selling links?
I don't think PR play anything into the site to make that the internal linking scheme work.