Nope. Don't see what you are saying. Maybe you should "rephrase" those statements.
But I guess you mean it makes no sense to look for a PR 8 domain and try to get a back link from it, when they'll place a link back to you on a PR 6 page?
You only get Pr from the page that is linking to you. If the site is PR8 but it is linking to you from a page that is PR4 that is the one that counts. So basically you get a PR4 backlink.
The common theory about PR is when you build links with high PR sites, you would get higher PR in the next update, the more build backlinks to higher PR sites, the better.