Recently I came across an interesting post by google guy, He agrees the Directory pagerank scale and the Toolbar pagerank scale are different,

This is an extract from his interesting post in forums.searchenginewatch.com

Quirk 4: "toolbar PageRank and directory PageRank can differ by up to two
units". Given that the toolbar and the directory go up to different maximum
values (10 and 8, yah?), and that in a fully incremental index, updates can
happen asynchronously in one area like the directory compared to the toolbar
display, this wouldn't surprise me an iota.

Your will be interested in seeing the other quirkes too,

Source: forums.searchenginewatch.com/showthread.php?p=23150#post23150

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