As most of you know, PageRank is an algorithm that calculates a web metric which shows how reputable a particular page is according to Google. This rank depends not only on the quality and the quantity of the incoming links but also on several other parameters such as the number of outgoing links per page (on the linking webpage), the position/visibility of the links and more.
We should note here that the real PageRank values are not the ones that appear on the PageRank Toolbar. The toolbar transforms the real values by using a logarithmic (or similar) scale from 0 to 10.
SEOs invented new PageRank Sculpting techniques and Webmasters became more careful on how they sell links (fewer and more relevant links per page, careful positioning, selling links for longer periods etc). At the same time SEO professionals started to analyze the Search Engine Results and came up with new hints on how to affect the rankings.
Additionally we should also take into account that the Real PageRank values are constantly recalculated and as a result the values that we see on the toolbar are old and not very accurate. Still when the PageRank Toolbar update is recent, they can give us a clue on whether our link building campaign is working.
Due to all these factors PR is more important over SEO.