No one is promising anyone future returns here.
Also, I'd argue that there are in fact central figures promising returns. You have all the big names. Andreas Andbopogogpffopolus, Gavin Andresen, etc. They're all very much claiming that Bitcoin is going to be the next big thing. And they're all huge holders of Bitcoin.
If I tell you that you will get a big return on Bitcoin, is Bitcoin a ponzi?
I'm just a random, ain't I?