Google Penguin update is related to back links, back links quality and lot of other factors..in simple if you have low quality back links, then your site will be penalized.
The new penguin is about backlinks. Quality, relative backlinks are welcome and non-relative, over backlink, Over optimization is goodbye.
According to penguin update, old school back linking strategy is no longer effective. Now comments should be relevant and quality should be high.
Google just watch their own business. they had described their rules and we are following these rules and work according. then what is the need to change these rules with out intimating us. If we used back hat methods our site or keywords should banned and de-ranked automatically.. know in last update made by Google in oct 2012 keyword friendly domains are effected..