I would say cryptocurrencies are like fiat money
Commodity monies (precious metals,
stones, or arrowheads) have values that are
independent of what they will buy. Fiat
money (paper currency) is valuable only
because it is money; its use is based on
faith.
Meaning their value is based on faith, faith tho the system creating the money, and faith to the people backing its value
Except devcoin is not just faith, it has investment in the future (through the bounties). I guess if you consider "believing in the future" some form of "faith", then yeah it's just faith.