pj beat me to it. in any economy, real or virtual, you need a collateral to back up currencies of any kind. if X country's economy is tumbling, their currency will lose value vs. other strong currencies (usually us dollar vs. euro, us dollar vs. yen, or say australian dollar vs. canadian dollar). when you are working with commodities (or bonds), there is a high risk involved in the price, as one tiny unexpected factor could make them go up or down. commodity traders don't expect to ever receive the actual product (oil, gold, pork belly, etc.) but at least when they trade futures, they know that in the very unusual case that they can't sell their future contracts before the time to cash them comes, they will receive the products. instead of trading paper, they would have to find a buyer for the product at whatever the price at the moment. in the bitcoins case, what would they receive in exchange if the price drops to floor levels?