Pr is not that important although it can be used for link exchange that can help for traffic. To get pr you need to build quality backlinks. Press release submission, Article posting and forum posting.
that is most common since most links (both internal and external) tend to point to the main home page.
Actually, this is backwards. If most external links point to your home page, this is a (somewhat weak) indicator of spam (or, technically, manipulative link practices for PR) in the way people like to imagine 1,000,000 links overnight might be.
It's completely unnatural to think of a person on their site saying, "I really enjoyed reading about X on Y's web site. See if you can find the page I'm talking about". Natural links point to internal pages - the one they're talking about.
that's probably because you are the only one building links to your website.
I mean, when people build link for the sake of links, they usually point to the home page. If a stranger points to your website, it will be check this guys' products/services, they are awesome and they will point to your product/service page or your "free widget" page etc etc...
those links will give your internal pages some PR.
