It's also obviously not true with even the tiniest amount of research. If you want to buy something online anonymously, then you use Bitcoin. There's the value.
http://money.cnn.com/data/commodities/
The reason I think it matters is that when commodities are used as currencies (e.g., gold, silver), the use value supports the currency value. If gold's value as a currency falls to zero, you can still make some nice jewelery. Whereas if people stop accepting dollars or Bitcoins for things you actually want, then they are basically useless.