Many people confuse Google PageRank (PR) with their page’s ranking for a certain search result for a certain keyword. Google PR is just one factor that is used to determine your page’s actual rank (position or placement) on a search results page for a given search query.
It is not uncommon to see a page with a lower PageRank value that is positioned higher on a search results page than a page with a higher PageRank. This shows that PageRank is not the most important factor in Google’s ranking algorithm. A properly keyword-optimized site with a lower Google PageRank can outrank a non-optimized site with a higher PageRank.
This is a common to many large corporate sites. The corporate site may have a high PageRank as a result of the large number of other sites that link to it, but they end up being outranked due to their lack of keyword optimization for their pages.