That is like asking KFC for the Colonel's recipe or asking Rolex for their blueprints. At the start there were a few days that the results fluctuated like that,and that caused panic. John then adapted the strategy to make the results more consistent while trying to maintain the average monthly growth. So exactly the thing that makes you skeptic made others nervous at an earlier point.
As anyone who have tried doing some serious trading knows, you can't just adapt away from the drastically varying Bitcoin market conditions and keep the profits. Of course if you're just making them up it's much easier to give the customers the numbers they want. I'm sure that in the next ponzi he starts he'll incorporate some of the criticism he's gotten while running this one. It's just too hard to do it now and still pretend to be a real business. For instance I'm pretty sure next time he'll say he's running bots, because claiming to do it manually is just silly.