>rankings are based on link popularity or PR
Partly. And the weight of PR relative to optimization factors is not the same for less competitive keywords as compared to highly competitive. PR counts, and links for this site are legitimately warranted because of cultural value as well as PR.
I don't believe it's the deciding factor in this case; at this level a 5 can do just fine. It's ranking for one keyword that's in the title which is also used on the page. But there's nothing for the others besides mention in the title. Title alone won't do it.
Simply put, the site needs some optimization done. There are 3 html pages. The rest of the site, including virtually all the keywords it can be optimized for, is all buried inside dynamic pages in the shopping cart.
The site needs some static HTML pages with a navigation system set up, at the very least using the keywords other than inside the shopping cart and page title, so there's something there to index. This one's not a PR issue, it's basic optimization that'll get it ranked for more.