You must read the rules first before join to a contest
Well he clearly stated this point :
Terms: If I don't receive any submits that are worthy/good enough for bitvest, then there may be no winners. Or only a minor consolation prize of .02 to .005 BTC if its
only minorly good. I have the right to determine which suggestions are unique and worthy of prize & which are not. For example suggesting implementing blackjack is a fairly common casino game,
and something I would most likely implement down the road, even though I implemented your suggestion, you wouldn't win in this case.
So this is not a scam or anything like this he was honest before people did participate!
Yes but sometimes the rules made by the organizers of the contest was very high and it looks just the way in which he is seeking profit rather than to give a gift, regardless of big or small he can from the intended site.