Above average volume does not mean trading to manipulate the contest. Other much more plausible explanations would be that:
--we have some really good stock pickers here who are good at finding stocks poised to move in the next three months. I know I look for a good company with some kind of "catalyst" expected in the contest period that will increase attention on the stock and hopefully price and volume. The nature of the contest makes this almost certain. Some of those catalysts never happen, and some of the binary event stocks end up with a 0 and not a 1, but it is natural for the top of the list to be comprised of stocks where the contestant got both the stock and the timing right.
--we have some people (myself included) who use the PSL contests an "idea lab" and make a point of researching all of the top picks (buying Mr. Sheep's picks for the last several contests would have yielded a solid return) and/or all of the picks from certain other successful contestants (so would buying KiK's picks, or Cl001's...). Some of this new attention translates to buying and a volume spike, often on stocks with not that much base volume.