Ponzi's are not a scam by default, just because the people playing the game end up losing in the end, that doesn't mean that there isn't a calculated risk that players can take with the hope to make money. In my opinion, ponzis with express written rules (like all thousand ponzis I've seen pop up) are not scams in themselves, nor when they close down, as long as they do so in a way that abides by what they have stated to the public. I don't think of ponzis any differently than dice sites.