the reason people see the resemblance between bitcoin's promotion and a classical ponzi scheme is that in both cases, the profit comes as a transfer of wealth from new participants to old participants, merely by convincing new participants to value the asset as an investment scheme on the hope of the cycle continuing. everyone here always says that's identical to shares in a new company, but shares in a new company become valuable (if legitimate) on the expectation of an eventual dividend. bonds become valuable because they will pay interest. etc.