Basically, in the term Ponzi that is, as you say, so liberally thrown around by people who do not really understand its definition, pretty much ANY form of "investment" could be called a Ponzi.

These same people would say Stock Market trading, Bitcoin etc etc is a Ponzi...they seem to think Ponzi is just something that "appears" to be too good to be true...in reality, Stock Market / Bitcoin / Gold / Silver / Your favorite celebrities worn knickers, whatever you are buying as an "investment" could go either way in value, up or down, and no one is saying Steem(it) is a certainty to go up, therefore, not a Ponzi...

One could speculate that Steem(it) will be a success and therefore, hopefully, the price will go up, but it might not (even if it is a success the price of STEEM and $S might not go up), no one is saying to throw your whole life savings into STEEM and you will earn profit (as far as I've scene at least)...