Why is this referred to as a "hoarding" problem? Why is saving not the correct term for this? To me, it's derogatory to call saving hording. At some point, the coins will be spent or sold. Hoarding is what those people on TV do, keep it until it is trash. Unless it's your plan to keep your BTC until you format them away, it's not hoarding.
Both "hoarding" and "investing" are forms of saving. A person that has savings can either "invest" it, and return it to the economy, or "hoard" it and remove it from the economy. It is a common term in economics and not meant to be derogatory (unless you are a Keynesian).
I would also like to point out that deflation by itself is not a problem at low levels. Just like you can have hyper-inflation where nobody wants to hold the currency, you can have hyper-deflation where nobody wants to spend the currency. Both are economic disasters. However, hoarding and deflation do not automatically lead to hyper-deflation, just as borrowing and inflation do not automatically lead to hyper-inflation.