Great presentation and analysis of your experiment. You have shared valuable conclusions. However my observations show that most of the sites that got penalized by Penguin had a backlink profile with the main keyword used more than 30%. So I am sure that keyword diversity and ratio plays a big role. Also sites with spammy links but which have used their main keyword under 20% of the time were not penalized.
How Google treats large organizations, which have media clout, greatly differs from small mom and pop organizations which do not have the media covering their every move. Although Google may publicly state that they treat everyone fairly, the Antitrust investigation in the US and elsewhere is a prime example of how Google's actions do not mirror that of their publicly stated principals.
Matt Cutts has noted that reconsideration requests are not accepted for Penguin related demotions as they are not manual actions but are instead algorithmically induced. Where Chrome, Overstock and JC Penny had manual actions taken against them for their practices, following the same recourse for Penguin affected websites will not work. A good read is here: http://searchenginewatch.com/articl...egative-SEO-Disavowing-Links-Bounce-Rate-More
...Matt Cutts has noted that reconsideration requests are not accepted for Penguin related demotions as they are not manual actions but are instead algorithmically induced. Where Chrome, Overstock and JC Penny had manual actions taken against them for their practices, following the same recourse for Penguin affected websites will not work. A good read is here: http://searchenginewatch.com/articl...egative-SEO-Disavowing-Links-Bounce-Rate-More
[*]Penguin is a very punitive update. It errs on the side of over punishment, rather than leniency, in order to aggressively combat web spam and reduce the profitability of SEO, possibly in order to compel people to use Adwords to generate traffic instead.