In many cases crying "ponzi" is likely an exclamation of "something wrong here" which your comment gives several examples. But cash, check and other instruments all have something wrong.

I'll suggest that the difference isn't that people know the details of how for example checks clear, few non-experts learn all the details, BUT virtually everyone knows where to go if there is a problem (bank branch). Most non-experts at this point in crypto currency would have no idea where to even go to investigate a problem.