Certain aspects of Bitcoin do appear to have certain characteristics of a Ponzi scheme in so far, as early adopters (people on top of the typical Ponzi-pyramid or Ponzi-row) profit most from it, if they decide to hold their coins. But Bitcoin doesn't need new people in order to work or in order to remain functioning.
okay then, i guess stocks are a ponzi scheme. also oil futures, or any other traded assets.
benefiting early adtopers is not a quality uniquely inherent to bitcoin.