Do you ever play RPG game like final fantasy ?Or maybe warcraft like DOTA? i have done some research maybe PageRank and Backlinks are connected with this. If you are a gamers maybe you will easily understand Backlinks is like experience where Pagerank is your level. Nah you need to get Experience from defeating enemy to get Level Nah it is the same you get backlinks and you will raise PageRank Then Like RPG games if you fight a better/stronger monster/enemy. You will got more experience . So do backlinks the same. IF you build backlinks from High Pr sites you will gain More greater quality backlinks for you to get higher PageRank After all the differences is Pagerank take 3months or major update from Google to update your real Pagerank.