That is a good point and that is a big weakness of bitcoin. Fact of the matter is this crazy appreciation is not very good for the currency. It encourages hoarding and discourages commerce. For all the stories about appreciation I do not hear many stories about bitcoin actually being used as a currency. And why would it be. Most people holding it believe it will go up in the future. Why would they spend their bitcoins on commerce if they think those bitcoins will be worth ten times their value in the future.

Currently bitcoin is not a currency but a very speculative investment.