Today's site with a PageRank of 0 could have a PageRank of 6 tomorrow. I've seen this myself on 2 separate sites - as they come out of the gate, they are graced with a PageRank of 6. Now, prior to that, any webmaster who was obsessed with PageRank would never link to that site. While the above mentioned scenario is probably not very common, the point is that while a site may be ranking low today, unless you know the webmaster personally, you don't know what other efforts that person is putting in to get that site ranked.

Another key element in consideration is that every unique link you get from a site counts. Whether it's from Joe's Pizza shop, or Pizza hut directly, to the search engine, they still count as two "votes" for your site. Now, each link would carry different levels of weight in regards to relevancy, but if you can't get a link from Pizza Hut, you could get about 1,200 links from the various Joe's Pizza Shops located on the web to make up for it.