This isn't true, if you are saving it you are reducing supply and driving the price up. This gives economic opportunity to other savers who at some point may try and build or sell something that has a greater rate of return than the deflation rate.
No, you're reducing the supply of the currency, you're not reducing the supply of stuff the currency can buy. If the amount of stuff drops but the currency stays the same, the price increases but if the amount of stuff the currency can buy increases but the currency stays the same (as in, the number of Bitcoins have capped) the price drops.
If other people build something or sell something they increase the supply of stuff which makes the prices drop if the currency stays the same. In other words, they're less incentivized to build or sell something (since selling and building has costs) than just keeping the money themselves in their mattress if the amount of currency is fixed.
