Now I believe everyone can agree that if this were a real bank and the bank stock has a non-0 value that each and every transaction would be valid and 'safe'. The USD note's from the bank would have a market value of about 1 USD and the purchasing power would be defended by the bank which would honor its IOUs. There should be no doubt that the USD would track real USD even though the bank never had any USD on deposit, only offsetting ledger entries and collateralized loans.
There are many difference between here the bank and Bitshare system, the bank issued USD notes with nominate price and it will honor its IOUs, but how about BitUSD? Its price will be solely determined by the market force and how can you say it will track the real USD?
I dont think BitUSD can track real USD only because of market force unless some connection between BitUSD and real USD is built, market is such a world that many factors have impact on BitUSD/USD exchange rate, most probably the BitUSD/USD exchange rate will behave like bitcoin/usd rate it will go up and down without a stable equilibrium.
In another word, why should BitUSD track USD and BitGold track gold? Can their name lead to a market consensus?
To enable BitUSD track USD, market makers is needed at the early phase, the market maker can do something like to sign a contract with some estore to purchase their BitUSD at a proper price, or even provide futures contracts to stabilize the price of BitUSD, some time later when a stable connection between BitUSD and USD has been built the market maker can escape and we can still expect the track relationship remains.