I believe that's called "an investment" -- you put resources in, hoping to get them back again plus more. The possibility of losing your principle is called "risk".
It's about as much of a Ponzi scheme as, say, a day at the track.
If you paid for a service, but got an investment, that's not exactly on the up-and-up. If that money is then used to try to work towards what they've sold you as currently available, that's not exactly a Ponzi scheme, but it does share quite a few similarities.
IMO, equating it to betting at the track isn't very accurate. Most people that bet at the track know they are taking on risk of no return, and what they gain for that is increased payout. Where's the knowledge here that you might not get what you paid for? What's the benefit of taking on this risk? Is it still betting if you buy something at a store and the shopkeeper turns around and puts the money into a slot machine before you've been given what you paid for and before know what's going on?
It's about as much of a Ponzi scheme as, say, a day at the track.