Many journalists have been lately saying that, but it seems they never cared to check fiat currencies.
The concept is absolutely the same.
http://en.wikipedia.org/wiki/Currency_appreciation_and_depreciationAnyone who read newspaper everyday, is probably sick of reading headlines like " appreciated with the entry of $? usd dollars in the country. Investors are optmistic."(purchase of local currency) or the other way around " devalued with the escape of $? usd dollars from the country. Investors in panick. " ( selling of local currency )
It is the same for gold etc. Before someone says that, gold has an actual use, but bitcoins too.
I think you're confused about what a ponzi scheme is.