>Ponzi schemes by definition hide the fact that there's any risk of non-payment
Ponzi schemes in general, yes. But, I was referring to this one, wherein it was out in the open.
>when you participate in a lottery you know - or can obtain - the odds of a payout up-front
Technically, yes. But, the odds in some games are so astronomical that knowing them is basically a non-factor. That is, people play completely hoping to get lucky, but not really expecting to win. I think the same applies with a Ponzi scheme like this one, wherein it's known that the music could stop playing anytime and the participants are simply hoping to get lucky.
Ponzi schemes by definition hide the fact that there's any risk of non-payment, that's why it's fraud, and illegal, and immoral.