That would actually be characterized as a pump-and-dump, not a ponzi. And if we used that term then we could at least debate the real question. Are the enthusiastic hype men actually cynical con-men trying to create greater fools so they can dump, or is the enthusiasm authentic by people who are genuinely long on bitcoin?
the two categories can overlap: if madoff's fund had traded in shares, it could have been illicitly pumped (and dumped) even whilst it was also a ponzi scheme.
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.
but yes, if you want to say that bitcoin is necessarily different from a classical ponzi scheme because there is no promoter who profits from investment fees tied to assets under management, then i would mostly agree. except that mt. gox comes pretty close.