First, in every banking transaction, both sides get to audit the results: the bank controls the electronic information, and the customer can check the bank's monthly statement against her own records. In e-voting, the County, and often the machine vendor, control the electronic information, and the customer (voters, watchdog organizations, candidates) cannot check the end result -- the vote tally -- against anything at all.
Second, banks operate in the free market. If you don't trust your bank, you can go to the competition. Elections, on the other hand, are by their nature run by monopolies. So while election officials have every incentive to make their elections run smoothly, the only outside incentives to make the process transparent and accountable come from watchdog organizations (such as VotePA) and active citizens.
As a Ph.D. mathematician with advanced training in computer science, I know that democracy can be accountable only if each citizen marks her intent on a record that can be preserved without the interference of technology, and only if the votes are counted in a way that every citizen may see and understand.