The biggest difference between them is that the fiat currencies have (arguably) a form of backing - the IRS only accepts its cut of the income of US Citizens in USD, regardless what form it was earned in. Even if a US citizen generates all their income by bartering, they still have to pay their taxes in USD. AFAIK, the same applies to countries in the eurozone. The US government spends the revenue the IRS collects on goods and services purchased from the general economy - also in USD, so USD has both demand for it, because it is the instrument one must pay taxes in, as well as demand for goods in services paid for in USD backing it. The magnitude of this demand is so enormous that the US Government can exist in a perpetual state of insolvency, and yet USD remains relatively stable in price.

All USDT has backing it are implied promises and advertising - which if you read the fine print you will know is false. If Tether turned out to be insolvent, how quickly do you suppose the price of USDT would collapse?

I know we've known that bitCNY/bitUSD, and more recently HERO, are the way to go for price-stable cryptocurrencies. I posted this to cryptocurrency, rather than BitShares, because a lot of people have yet to discover this. What we really need though, is to try to get some exchanges (in addition to Bittrex which has a BTC:bitCNY pair) to list them. In a saner world, it's marketcap would be occupied by smartcoins.