Cigarettes, cans of smoked fish, Lego sets, bottles of Liquid Tide, fifths of Jack Daniels, shotgun shells, promises to repay favors, and much, much more can be used as money.

On the other hand, the USD, EUR, JPY, and all other pure fiat currencies are terrible stores of long-term value. Thus, they fail to provide one of the most basic functions of money.

Also, try using pennies to represent unique debt contracts, shares of stock, insurance policies, etc., as one can do with colored coins; or try organizing a 2-of-3 multisig USD.

All this talk about money/is-not-money distracts from the fact that bitcoins are unspent transaction outputs, and that everything that virtually everyone says about them is metaphors. Bitcoins are bitcoins, and they don't fit neatly within existing statutes, regulations, or administrative rules.