Web_speed - 2:13 am on Jul 20, 2012 (gmt 0)
Google has massively increased the number of changes they introduce for the past couple of years. Considering this, I don't think it would be that easy to tell the correct reasons for the OP's question, though he has given a detailed account of his new launch.
IMO, call it what you will, I've seen enough of this to call it by its real name, "shuffling". Pure random shuffling designed to keep everyone guessing, bleeding and ad spending... good luck.