This:
There is no nominal value, they start out valued just like bitcoins did.
BTW, bitcoins were valued in bitcoins. In BitShares you value BitUSD in FedUSD!
And this:
So, by this simple analogy, I hope I have shown that the BitShares system is really no different than existing banks except that instead of issuing new USD with your house as collateral, it issues new USD with the bank stock as collateral.
So, there is a big difference and this simple analogy is not quite useful.
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Aside from price oscillations around parity there is only one way to keep the value of BitUSD equal to FedUSD. To issue 1 BitUSD if you get 1 FedUSD and to pay out 1 FedUSD when 1 BitUSD is redeemed. FedUSD units are not part of any block chain for they are property of Federal Reserve. Where FedUSD units in the BitShares system reside?