emugoo, you are talking logically. And that is what a business would have to do... But now think of what is happening bitcoin users are paying upwards of 10-20% in "transaction fees" why would anyone do that when you can just pay direct in USD or whatever I will be eventually converting that money into?
One of the foreseeable benefits of bitcoin is that the fees could be really low, potentially lower than current transaction fees of 3-5% which credit card transactions are. If people are exchanging back and forth between a currency and bitcoins its defeating everything: 1-2% to convert cash to BTC, 1% transaction fee (0.01 BTC or hopefully less someday?) and another 1-2% to switch back into cash. Thats not how any business can or should operate.
The only business that is profitable and efficient with bitcoin is accepting bitcoins, and then using all of those bitcoins to buy other goods and services. You should never be exchanging back into dollars.
And XLCUS you are right, there really is no way to stop people from doing it. By the same vein that "the majority" of people will just use bitcoins as a stock-market style gambling game, instead of using it as a currency to buy goods and services. It would be hard to stop it from happening. So if this is the case, then there really is no way to make bitcoin work as a currency.
Jonathan, if you wanted a "trusted bank" for bitcoin that could entirely be possible. Someone could hold all your bitcoins for you, and you could tell them who to pay and when? But trust is really relative. For some reason you trust real world banks, which are just another corporation. (I personally dont trust them anymore)