New categorization might be good, but what exactly distinguishes a Ponzi-type game from other gambling?
Ponzi is a pyramid scheme. Also, these operators create outlandish rules where if you don't deposit in certain time frames, you don't get any BTC back. That's not gambling. That's stealing.
At least with other forms of gambling, the system is "provably fair" to an extent.
I suppose technically it's gambling. You deposit a sum of money that you might either lose (no more investors, or owner runs off with your money) or win, and gain a profit relative to the amount deposited.