I don't know why you're being downvoted: You've hit the nail on the head - Bitcoin is a Pyramid scheme, not a Ponzi scheme.

I've been seeing comparisons to Ponzi schemes a lot in the last few weeks. AFAICS "Bitcoin as Ponzi scheme" is a useful strawman for pro-bitcoin arguments because it's so easily defeated. Bitcoin as Pyramid scheme is a much stronger argument, with far fewer articles dedicated to it.