This isn't so much a Ponzi Scheme as an elaborate form of gambling, however. The rules are outlined transparently and precisely, so I believe it would better fit under the laws that govern online gambling. Ponzi schemes fall under fraud laws, which I do not think should apply.
IANAL, however.
Online gambling (in the United States at least) will get you immediate scrutiny, and ultimately you will be shut down. It is super unfortunate too because I am a firm believer that any adult should be able to do whatever they choose to do with their own money (as long as it doesn't harm someone else)