Note the circle on 'US Data Only'. Global data isn't stellar either:
View Screen Capture
Since all data is pretty much based estimates, its a rough indicator on the fortunes of a site. So you can say a certain peak is because of a certain event. Regarding the freedies voting traffice, AFAIR there was a link at the end of the ballot that gave you the option to visit MP and win an ipad. I doubt everyone followed it after the vote?