Popular websites/blogs have dropped page rank

Some major websites/blogs have gone down in their page rank. There's going to be a lot of speculation as to why these sites were dropped. And needless to say, the discussions will be interesting.

Here are some popular sites that have gone down in Page Rank.

http://www.yahoo.com PR10 to PR9
http://www.techcrunch.com PR8 to PR7
http://www.engadget.com PR7 to PR5
http://www.johnchow.com PR6 to PR4
http://www.problogger.net PR6 to PR4 but later returned to 6
http://andybeard.eu PR5 to PR3 but later returned to 4
http://www.copyblogger.com PR6 to PR4
http://www.forbes.com PR7 to PR5
http://www.entrepreneurs-journey.com PR6 to PR3
http://www.quickonlinetips.com PR6 to PR3
http://www.johntp.com PR6 to PR4
http://www.autoblog.com PR6 to PR4
http://pingoat.com PR6 to PR4