OK, I "confess" that I downvoted your post because I considered the question disingenuous. The risk/reward may not always be clear to all participants, and in a fairer world such choices might not have existed in the first place.
My vote is really against encouraging people to view design contests as fair enough, not you personally.
They didn't "work for free", they made a decision that the risk/reward was worth it.
Oh, and if you down-vote someone on HN for asking a question the least you can do is fess up and explain why.