I thought Google was the only site with PR10. Even eBay and Yahoo have only PR9. But today when I happened to visit statcounter.com, I noticed they have a PR10 too. Are there any more of such sites?
My understanding is that PR10 is granted by hand ... which is why the list seems a little strange (e.g. Keio University is listed with 4020 backlinks, yet Microsoft is excluded with 119,000 ... as are other PR 9 sites that have tons of backlinks).
In retrospect it should be obvious Acrobat is so highly ranked. Every time a website has a .PDF, there usually is a link to download Acrobat.